I'm not sure about it too much. My Betta SEEMED like he would be really aggressive because he was CONSTANTLY flaring. However, I put in three ghost shrimp and he hasn't been agressive towards them at all. He did and does go investigate them from time to time, but never has he attacked or nipped or anything like that. He usually just swims down right next to them and watches.
I also keep a few plants, but nothing they can hide it too well, and my tank is 5 gallons.
I've also read ghost shrimp need a little salt from time to time, so don't forget that.
I'm really glad I got them, though. They make the Betta tank even more exciting.