My lionfish is about 5" long and hasn't bothered my cleaner shrimp in the year since he's been there. As long as your shrimp stays big enough, there shouldn't be any problems - they only chase things that are small enough to swallow.
I've been poked by dwarf lions a few times and, while it hurts, it's not too bad. Feels like a bee sting. You have to work pretty hard to get stung, though - they're very passive by nature and will keep their distance if they feel threatened. All of my stings were from grabbing them during capture.