Most of the time the nem and clowns will ignore each other, but a guy on rc had one hosting his flower nem and posted a pic. I'll see if I can track it down, definitely possible though and I'd love if mine started trying to host. When they eat fish it's usually either one that was already sick or one that got spooked and ran right into it, so if yours are testing the waters they're probably just seeing if it will host.
That said I don't know a ton about nems and hosting so I'd ask on the nems forum on rc to be sure.