I evaluated the JBoss IDE 1.5.X for EJB3 reverse engineerin on callisto (eclipse 3.2) and it seems to work fine.
We do integrate portions of JBossIDE but I believe using the newer version along side MyEclipse 5.1 should work… you can try installing it and making sure that the functionality you will be using of both products continues to work.
Also our plan is to start supporting JEE 5 in our next major release, but exactly *what* and how it is supported hasn’t been decided at this moment.