Pistol shrimp are harmless. I even purposely bought one for my tank at work with a goby. I thought he was dead since I hadn't seen him in a year but I got lucky the other day and glimpsed him peeking out from behind a rock...
I don't want to be all "kids these days..." but... Back in the day we fought mantis hitchhikers and aiptasia all the time, and we were glad for the privilege to serve our tanks!

Back then we didn't have fancy lasers and copperband butterflies to kill the aiptasia; we strangled it with our bare tongs. Back then the only good mantis was a dead mantis, but now you have people who actually want to keep them as pets and will give you money for your pests!
But seriously, diversity = stability. I just don't think you can purposely "import" enough diversity to create a stable ecosystem in your tank. Parasites sneak in all the time on everything else we add to the tank. It seems a bit unfair to blame live rock when we still wind up with nudibranchs, redbugs, aiptasia, and pyramid snails on frags coming into our tanks.
The discussions in this thread, and the pictures especially, have me really leaning towards pulling the trigger on some FL aquacultured rock, unless Premium Aquatics gets some Manado rock sometime soon... Maybe I'm just too old-school with my fond memories of red flashlights at night playing "what the heck is that?!" in high school...
The only thing I'm really worried about are cirolanid isopods... Those actually seem scary and hard to deal with, unlike gorilla crabs or mantis...