No offense to the "fine in a 5 gallon" but please remember there is not enough room for two in a 5 unless it's divided tank for two bettas. Frogs poop too, y'know
ADFs can become very stressed if they are close to a possible predator, without having sufficient hiding space. Mine liked to do sky-diving poses in the plants and under rocks :) I had him in a 10 with my betta, and even then he still munched my betta's tail.... Very important to have sufficient space to meet the demands of both critters.
Feeding: Fast sinking pellets, or even using a thin baster to grab a flake or whatever and "spit it out" infront of his face... That is what I did. I distracted my male, and either plopped down bottom feeder wafers, sometimes greens, and flakes/pellets through a baster to my froggy.
Aggression: They are generally friendly, but like I mentioned they may munch the fins... So allow enough space for both! Bettas can be poops too, so give hiding spots and soft or real plants. Make sure to get ADF and NOT the African Clawed who get bigger and are much more aggressive.