I do not recommend shrimp. They'll be a snack =D he sounds like my Sasuke.. mean little guy. I've got each betta to their own accord... Spartan is the anything-goes, Sasuke is the nothing-but-maybe-a-snail-that's-bigger-if-lucky, Madame the snail murderer cannot have anything, Maine the bully, El Dorado the anything-goes...
If you know your betta, you'll know how compatible. :) some of mine shouldn't be with shrimp, but a snail is fine. So... you gotta use your discretion :) Be aware African Dwarf Frogs like to be in twos or more, plus I had one who munched on my poor betta's tail.
Some bettas sadly are just deemed the nothing-fish.. meaning there is nothing you can add >< other than plants and ornaments.