Honestly I feed some of my wild species of bettas nothing but live blackworms, whiteworms, frozen bloodworms and frozen brineshrimp with the occasional feeding of pellets in between. I have never had an issue with constipation or blockage because of their diet. In fact they are some of my healthiest fish and are always spawning or sparring.
As long as you are not going overboard and your betta doesn't look like it has swallowed a marble after feedings, frozen bloodworms are a readily accepted treat by most bettas.
I don't like freeze-dried or flake food as I feel that does have the potential to cause issues, but if you are mindful of the amount you are feeding, frozen bloodworms are perfectly fine.