Tank bred doesn't have anything to do with it. It's an instinct for them to feel secure but that doesn't mean they will choose a nem in our tanks over a powerhead, a heater or just a corner of an aquarium. The nems sting is what seems to draw them in though.
My clowns are captive bred and they had never seen a nem until I added a haddoni carpet. Somehow the female knew what it was almost instantly and went out of her way to keep the little male out of it (had she not, the carpet probably would have eaten him). She spent the next several days mouthing the tentacles and slowly pushing her head in without going all the way in. Eventually she was "all in" and started to show the male how to acclimate himself to the nems sting. Unfortunately the nem took a turn for the wosre shortly after and I lost it. After the carpet died, they went back to their corner rock.
My clowns are captive bred and they had never seen a nem until I added a haddoni carpet. Somehow the female knew what it was almost instantly and went out of her way to keep the little male out of it (had she not, the carpet probably would have eaten him). She spent the next several days mouthing the tentacles and slowly pushing her head in without going all the way in. Eventually she was "all in" and started to show the male how to acclimate himself to the nems sting. Unfortunately the nem took a turn for the wosre shortly after and I lost it. After the carpet died, they went back to their corner rock.
I'm glad everything seems to be working out. 
