I worked out why this keeps happening. Basically alot of ant keepers use similar ant farms/nests etc with a similar smell and feed exactly the same food, eg frozen crickets and honey. All this creates a similar nest smell, and as we all should know ants tell friend from enemy by smell, so thats why wildly different species are sometimes accepting each other.
Accepting each other is hard to say, but its true what you are telling, the smell of the ants in captivity, kept en fed in the same room with the same food makes the smell of the nest fades away so they all smell (a bit) the same. Still in most cases when ants from other spieces meet they will fight.