Yes, you can run both WLS and JBossAS in the same host. Some things to look out for:
1) Make sure there are no port conflicts. The file docs/examples/binding-manager/sample-bindings.xml lists the ports used for 4.0.x and 4.2.x (for 5.0, see server/xxx/conf/binding.xml)
2) Make sure you have enough memory - you will now have two JVMs running.
Thank you for such a quick response.