LoL! Well that's not the purpose of me wanting one! :)
My X had a tank with spotted puffer fish and the idiot at the pet store told us that fiddler crabs would be fine in the tank. Well, we dropped them in, the puffers nudged each of them 2-3 times in curiosity, and they went belly up. They basically were given a heart attack with 1 quick nudge. They lasted a whole 45 seconds in the tank. :(
My betta is a wimp! I have never seen him flare and he tends to hide from his tankmates. He's like the Labrador retriever of bettas.
I said earlier on here that my Hughie is like a lab puppy, goes belly up and pee's himself if you pay him attention haha Your boy sounds like mine!
I have no advice though, I have seen them in the pet stores but not in person. Someone close to me owns and breeds them, but I never took a liking to them. I am not going to Google them though, or I'll have one by the end of the week!
fiddlers aren't fully aquatic, they need more land/sand then actual water- they'd drown without acess to air/land. Both crawdads and fiddlers are messy as heck, though crawdads are freshwater and fiddlers (I'm pretty sure) are salt water. Crawfish are pretty agressive, especially as they grow bigger, so neither of them are very good tank mates.