Belated follow-up: In case anyone is interested in how this turned out, you can in fact keep a betta with tadpoles. He nibbled one when I first put him in, but it must have tasted horrible because I swear he made a face and has never done it since. He's not even that docile of a betta, as all subsequent attempts to introduce him to either of my community tanks failed miserably, with much violence.
The tadpoles themselves seemed to do well. I fed them some tropical crisps that would sink as well as small pieces of sinking algae wafers. They liked the former a lot more. I identified them as American Toad tadpoles, which turned out to be spot on, and quite a few turned into tiny toads very quickly, and were released into the wild (or the rooms of a few certain people in the dorm, but you know how it is).
Some of them drowned after growing front legs. Not too sure how some were able to handle the island I had and not others, but I switched to a makeshift island with a smoother grade and a better gripped surface and that seems to have fixed the problem.
I still have a good dozen stragglers that haven't made the full change yet. Most have a good set of hind legs growing. There are a few runts that appear the exact same as when I pulled them from the puddle. No idea what's up with them. If and when these all turn into toads, I'm not too sure what I'm going to do, as it's getting cold enough here that releasing them would probably be a death sentence. Turtle food maybe? (Not that that wouldn't be a death sentence too, but at least the red-eared sliders would get something out of it.)
The betta is doing great, though. He's bright orange, and since I got him when I was in a pre-Hallowe'en mood, I named him Amontillado (Pumpkin and/or Jack seemed too obvious). He's been completely unruffled by the somewhat disturbing nature of tadpole waste, which puts an oil slick on the top of the water. The tank always smells like pond-water too, no matter how often I clean it. Roommate less than pleased, though she was placated by the toad-in-friend's-pillowcase maneuvers on certain targets of hers.
Hope that report helped anyone who ever feels the urge to collect some tadpoles. It's certainly been an adventure. Oh, and red-eared sliders love to eat tadpoles. Love them. They're turtle crack.
