If your bettas are anything like mine, they'll eat anything if it's chopped up small enough. Give it a try though, I don't think it would be bad for them...
Cute! Jerry follows my pen when I write... and flares at it if he's in the mood. I might try the raisins with him... I can't imagine him turning down food.
You might want to be careful though, raisins can be fatal to dogs. (Yes, I know they're completely unrelated species, but I wanted to give you a heads up just in case.)