IME, fu's pretty much keep to themselves being bottom dwellers, and they don't seem to bother other bottom-dwelling species as well.
There are a few folks here that have mixed a fu, a fuzzy, and a zebra with good success. In fact, depending on how solidly your fu feeds, it may suffer in food competition, or it may step up to the "challenge". We target feed our multiples, so each fish gets its share.