They're about as hardy as a cnidarian can get, IME.
A few weeks ago, my girlfriend added a third to her tank from an LFS. It was a gorgeous bright green and yellow specimen that was in the process of splitting, and in an attempt to break off the chunk of rock it was attached to and give us both halves, the nem ended up being rather brutally ripped in two.
He gave us the larger chunk for a huge discount. It wasn't even close to round, about half the foot was gone, it was torn all the way to the mouth, and had a big diagonal slice into the oral disk.
It took about 20 minutes to plant itself instead of the 5 I'd usually expect. The sexy shrimp spent about 45 minutes cleaning up all the excess mucous around its wounds, and then it started to open up a bit. It's now completely healed, nearly doubled in size, and has moved to a spot that it like better than where it was initially placed.
I have one in my tank that has taken up residence almost completely shaded under an overhang. It gets far less light than my LPS corals do, but is still quite happy.
They are generally far more sticky than even tube anemones. Careless fish will be easily caught and killed, but in my experience most fish tend to do a good job avoiding them.
My girlfriend will be adding a pair of young ocellaris clowns to her tank with three of them in a couple months time. We're going to try to get them to host in something else in the QT first, but I am a bit concerned about it.