They may or may not. Clowns are odd, especially ocellaris. I have had them host all sorts of euphyllia, Duncans, and even heaters. Some may never host in anything, like my Mochas, who have shown no interest in hosting anything at all. If you do get a nem, you want to be mindful that they will move on you and will cause issues with the corals when it does. This is especially true of when first putting it in the tank as the nem will seek out the best spot. This can sometimes a couple weeks or more before it finally settles in, and this may only be temporary. Various nems especially bubble tips are known for going on walkabout and will at random times mozy all over the tank only to end up in the same spot as before. Another consideration is powerheads and nems don't agree with each other, so if yours have wide spaced fins, then you may want to look at getting a foam guards for it. There's nothing worse than coming home to see your nem half sucked into the powerhead inlets....
All that aside, there are ways to get your clowns to host the nem provided it is large enough and a variety that is considered clown safe. First method is to get a large colander and zip tie some pool noodle floats to it so it will well... float. heh.. Catch the clowns and put them in there with the nem. It may take them a few hours but at some point they will figure it out and start hosting in it. Once both are actively in it give them at least an hour or more before moving it. When ready you can carefully detach the nem if it has grabbed hold of the colander and then transfer it to the tank. The clowns should seek it out and stay with it as it decides to attach. Just be sure to turn all flow off at this point so the chances are much higher that it will attach where you move it to. When you release the clowns back in after the nem is secured try to do so near it so they see it and should be drawn to it.
Another option is to get a large clear acclimation box and catch the clowns and put them in there or skip the box and put them in your sump. Leave them in there for a couple weeks while the nem decides where it wants to be. Once it has settled in, get a large clear acrylic tube and position it just above the nem. Now take the clowns out of the sump and release them in the tube and using a turkey baster or something to create flow to gently push them down the tube directly into the nem. They should instantly get the idea and stay in or around the nem from that point on.
