I cant see a problem, we have a pair in a 4x2x2 with 3 breeding sized Frontosa's and they are fine.
They are generally very very peaceful but our male is nasty, he got kicked out of our main tank for fighting with the electric blue Jack Dempsey.Anyway thank god,the frontosa seem to have pulled him in to line.So yeah ,if you ever want to put it in with any other large blue fish,just keep an eye on it in case.
Bren