It's extremely common to feed them blood worms. It's usually recommended to not do it too often. You could feed them blood worms every other day if they have sufficient fiber on the off days, but they'l just get chubby! Maybe 1 or 2 times a week would be good. Frozen brine shrimp is even better, it has fiber and protein.
ADFs are commonly fed blood worms as a pretty normal diet. I would be worried if I had ADFs with my sorority, my bettas tend to pick on anyone in the tank that can't get away or doesn't have sufficient protection. Tank mates I have are ghost shrimp (hard for bettas to see, can move fast if they need to if the tank has sufficient room), Corys (armored and has mild poisen, mine aren't afraid of the bettas at all and bump into them occasionaly. My bettas have learned to leave them alone), Nerite snails (only a few of my bettas tried to bug them in the past, but they're so well armored it's useless). Dwarf frogs are very slow and shy.