Having similar issues at the minute myself, actually. Just got an ADF on Saturday but I'm not sure he's eaten anything and the betta is getting too much. I have always feed my betta bloodworms with tongs, so they already know to look out for it and he's too quick for me to get anywhere near the bottom of the tank without him nabbing it (it's only a 5.5g). Also having a lot of trouble even locating the frog. I've a fair amount of plants and a decent sized piece of spider wood, all of which provide very effective cover.
That might be a blessing, though; Sagat's not as aggressive as Tong Po but neither are most piranha. TP will kill or be killed by anything that goes into his tank, for sure; Sagat's always seemed very calm by comparison.

Sagat's been stalking and flaring at the frog, though. I saw him try to bite at the frog's leg when it was poking out of a plant but the frog is unharmed; still got the full webbing and moving normally. I only saw the frog twice briefly for all of yesterday, though and I was sitting next to the tank most of the day.
I do have something to try, though; got a spring-loaded 'tube within a tube' device, so you can put stuff in the interior tube and then when you press a button, it's released. The betta hasn't seen it before, so hopefully he'll keep his distance but it's finding the frog in the first place that's the current challenge. He surfaces now and then for air, but that's a split-second jumping out of the middle of an anubias bush or something then away into the undergrowth again...

I figured it out!!! I use pipettes instead of tongs. I used to use tongs but feeding other frozen foods is easier with pipettes. Wish I knew how to make a head-slap!

Pipettes allow you to drop one piece of food at a time. Last night I dropped Krill in Esmeralda's mouth and while she chewed I did the same for Clayton. Also, because your hands are right there, the Betta doesn't get close.

To feed the Betta (which I do first) I barely hold the end of the pipette under water and the Betta pull the food from it or if it's something not long enough for them to pull I squirt the food on the opposite side of the tank. Then I feed the ADF and other critters while the Betta is eating or chasing the dropped food. Hope this makes sense.

10pcs 5ml Disposable Plastic Graduated Dropper Transfer Pipettes US Seller | eBay

They're also great for dosing ferts, Prime, etc., if you get the 5 ml size.

Unless you have at least three ADF you won't see them much. They require others of their kind for confidence because they are so shy.

Keep me posted and let me know what you find that works!

Re flaring and stalking: Hm. One of the frogs nips at the betta if he ever gets too close, so he keeps his distance and flies off if a frog comes toward him. He's just a chill betta, though, I've never seen him flare, stalk, or bite at anything in the tank.

Re finding them: I wonder if they're concerned because of the betta? My two frogs have been very active and out and about since the second day they were in the tank, they just hid the first. Sounds like you have good hiding places for them. I'd like to get a a couple more for their comfort, but first I need to be sure I can feed them! This 'one at a time' feeding thing doesn't lend itself to four frogs.

Re feeding: Last night I put my betta in a mock 'breeder box' aka tupperware balanced on the rim of the tank, took a small jar, filled it with defrosted frozen bloodworms and pellets, and put it on the substrate and encourage one of the frogs into it. He sat there. And sat there... I don't think he quite got the idea to eat the food, yargh. But it might be something to try for yours so that he's protected from the betta while he eats?

I'll respond to the pipette idea below-

Neat!! I used your link and bought some. Will try it. Thanks for the detailed description. I tried a syringe, but it wasn't like one worm at a time, might try that. Last night, I tried putting worms and bites in a clear jar last night while the betta was in a tupperware in the tank (balanced on the lid rim) and put a frog in there- but he didn't notice the food. It would be great if I could just stick food in a jar, stick the frogs in the jar, come back 15 minutes later and they'd be fed...but doesn't look promising.

Looking forward to trying the pipettes...

I am so sorry! I can't believe it took me this long to remember the difference between using pipettes and tongs!

Thank Esmeralda and Clayton because feeding them last evening reminded me. And I hope the pipettes work for you as well as they work for me.

Oh, and you can feed strictly frozen to ADF. You might try soaking the bites in a bit of garlic juice so they smell stronger. I use pill bottles for everything. The reason they go for your Betta's caudal is the ADF are so blind that any movement they consider food.

Well, the spring-load tube thing worked well and I found out where he's been. Big bit of driftwood is actually kinda hollow and he can get under it. So, I waited until the fish was occupied with floating pellets and dropped some bloodworm with the tube near the 'entrance' to his hidey-hole. He came straight out and grabbed a piece. Then the fish noticed, made a beeline for it and ate the rest of the bloodworm, then burrowed the substrate out of the way and forced himself under the driftwood to chase the frog. Haven't seen the frog since, kinda worried he's either been hurt or he's now hiding deeper under the wood and won't be able to get out for air. Overall, not a good development. I think I'm going to take him back if things don't get much better by the end of the week; even if he's OK, I can't keep him running and hiding his whole life with the fish stealing his food the whole time.

Unless you get more ADF he will have a sad life even if the Betta weren't in the tank. Sorry to be so blunt but that's the way of it. Even people who have an ADF-only tank are advised to keep no fewer than two or three. When you add tank mates that ups the ante.

Hm. Hope things improve and the betta loses interest.

I'm optimistic about the pipettes, thanks.

Last question, I swear! How long are frozen blood worms defrosted with a bit of tank water, kept in the frig in a covered (in my case, baby food jar) good for? 3 days? A week?