I have heard that they will move around until they find the spot they like and then they will not really move after that... but then you always have to consider what happens if they become unhappy with that spot. I think it can be done if you are prepared for it. I saw someone who had half their tank full of nems and the other half coral and they had powerheads blasting the middle so that the nems wouldn't cross over to the other side. Where there is a will there is a way.