Actually, my coral banded shrimp picks parasites from the inside of my radiatas mouth. My cleaner shrimp and my radiata have fin/antennea wars, but the cleaner is afraid of him, so they never really mess with each other. I've also had peppermint shrimp walk right on his head, and he hasn't even snapped at them. Now it could be that I just have a very passive radiata, but I also have a fu manchu in the same tank, and he hasn't bothered any of the shrimp either.
About the stinging, you can actually see the venom when they eject it, it looks like their fins are weeping ice...but it's not there all the time, they either have to be stressed or frightened...or, most horribly and sadly, dead...I think it kind of leaks out.
About feeding: They will take anything that *moves* I have yet to see one eat anything sitting still...and I have three now, and did have another volitans (died within 24 hours...I think that he just didn't ship well)