Can you enumerate the incompatibilities that you've already found? I too am trying to mix the two.
It may support AS 5 is the best we can say at present.
This is something we are going to look into but the main focus of ESB 4.x is currently the AS 4 stream, specifically AS 4.2.3 for the ESB 4.5 release. If the changes are not too invasive then it should be possible to make it work on AS 5.