you will find that many things in this hobby are much more tolerant of each other when allowed to grow together, rather than be placed near each other to grow.
that said, Ive only had one nem in this hobby and it is a condy..........I have had it and its clowns for many years and I have polyps amongst other corals that are within its reach and get touched by its "deadly" arms every day. I dont think they like it but it doesnt seem kill the things that have slowly encroached its territory wheras anything placed within its reach is of course toast. It very well may be not so much that the coral can take it, as it is the condy doesnt feel threatened by something new....dont know