I am using Seam 1.0 / E-EJB Alpha8 / Tomcat 5.5 with Eclipse 3.1 / WTP 1.0 in a Dynamic Web Project and this is similar with what you describe about IBM RAD, but is very bugged and works mostly for content, not classes.
About JBoss IDE, this shoud be explanatory:
using JBoss AS instead of E-EJB / Tomcat.
and Eclipse 3.2 / WTP 1.5 and JBoss IDE 2.0 will arrive fist week of July, I hope.
Cavani, thanks a lot