IMO they are reef safe. I've had one for about 7 months. They tend to hide quite a bit if you only have one. I have 2 cleaner shrimp the fire shrimp hangs out with so I get to see it a lot. It is my favorite shrimp and the only the tang will let clean it.
I've had my fire shrimp for about 9 months now, it does stay under the rock most of the time however it comes out when i feed the tank. It scurries around like it's on crack or something until it gets hold of a chunk of food and then he's off to the hiding spot to devour it. I could live with or without it although i really get a kick out of my sister when she sees it. When it scurries all about she really freaks out cause she says it looks creepy. It really cracks me up