I guess it depends on what you mean by "false" clowns. When referring to clown fish, people generally are talking about Percula clownfish. False are Ocellaris clownfish - both are very close relatives. Many fish stores sell Ocellaris clowns as percula, but you can tell my the amount of black that exists between the white and orange on their bodies. The thicker tha lines, better chance you have "Percs". I have a pair of "false" clowns - ocellaris - and they hosted in my BTA three days after putting them in my tank. They currently host in three different BTA's. I have found no problem with them hosting, especially if they are from the ocean. It may take a few weeks for farmed fish to host, but the instinct is still there. IMHO. Hope this helps.
-Dr Marco :sfish: