I don't see why you can't use them if they can support some type of hang-on-back filter. However, one of the reasons you QT fish is for close observation. It may be hard to see the beginnings of ich if you can only sort of look down on them and not get a good side view. Before you decide to transfer them from the QT to the DT, I'd scoop them up in a glass container of some sort and give them a real close look-over.