Ya i was wondering that aswell because i my bromeliad is potted in the greatstuff and im afraid of it getting water logged and dieing. For now the charcole in the potting mix is working but it can only hold so much.
I tried, but it didnt work out very well. The pots i used before i foamed the aquarium were probably too small. Now the cured foam completely smothered half of them, and they are lost in the background somewhere. I dont want to cut the foam back up, so they are just stuck there i guess. They add some texture to it though.
If i were you, id use fairly large pots, and stick them on After you apply the foam (while its still curing) not before. Then after the first layer is cured, cover the rest of the exposed pots with a thin layer of foam.