Then again, some bettas are perfectly fine with shrimp. My boy is very content to ignore his red cherries (different coloured cousin of the blue velvet shrimp). He will swim up to them and continue on or swim by and brush them with his fins and it neither bothers him, nor the shrimp... they just continue eating whatever it was that they were eating before. I have these bright little guys in a very heavily planted 5 gal NPT with lots of cover, small holes (too small for bettas) and the cover is at all levels of the tank. I also added the cherries to the tank, and didn't add the betta for about 48 hrs and I already had a pretty good idea of how he'd react: I had found a pond snail in his temp bowl... he sniffed it, it moved, he swam off very quickly to his cave and I didn't see him for an hour or so after that. LMAO, my betta's a wuss.
As I said in another thread, bettas are like dogs when it comes to tank mates: some will do just fine with a cat, some will chase it and harass it, some will be terrorized by the cat. It all depends on the dog. Same with bettas and shrimp: some will be fine, some will harass or even kill and/or eat them and some will be stressed out by their presence. You won't know what your betta will be like until you try. But you have to be prepared for all outcomes in case things go south, so to speak :)