It probably would be easy enough to try in a minute or two.
Only thing to worry about are possible port conflicts, such as 8080 in JBoss clashing with 8080 on Websphere.
As genman points out, most of the ports used by WAS and JBoss are the same. You simply need to make sure there are no conflicts in HTTP, Naming etc.
Have a look at:
This gives a list of the applicable ports used by JBoss. As long as there are no conflicts with WAS you should be all set.