Bettas should not have shrimp in their diet more than a couple times a week as it is not considered a complete food for them after their initial fry period. It is too rich for their tummies and they will not tolerate it much for more than an occasional treat but not a meal. Some will not even eat it unless it is a live one that lives in the tank with them.
That is NOT a good idea.
Almost every betta will eat bloodworms and love them but be prepared that sometimes when they have had them they will not return to the pellets or other food, as they are actually the bettas favorite food. Or at least that is what happened with some of mine. Do be careful not to overfeed with whatever you feed. Overfeeding is so easy to do with a betta as they do not have an "OFF" switch. They will eat until they are ready to pop and that is not good for them. If you let the fish determine what he wants to do he will overeat. You have to be the boss and contol the eating. A small pinch of food twice a day is all they need. Pellets really need to be controlled as they are mostly made of meal and have a lot of nondigestible material in them.
Rose