I have seen a male dovii kept with other fish. I have been at a pet store and they had a 300gl display tank. They only had driftwood on the sides of the tank and the rest was open, so none of the fish could really have a territory. The dovii they had was about 13+in and they had a red devil, green terror, jag, trimac, buttikoferi, some vega sp, and about 4 or 5 other fish as well. All of their fins were basically perfect so you could tell that there wasn't to much aggressine. But the tank was pretty packed as well. I asked him how he got them all to cohabitate so well and he said he added them all at once and never changed the tank around.
So you can have tankmates you just have to do it right.