I've had a jruby rails app deployed to jboss for quite some time now. For grins and giggles I decided to try it under Glassfish today. After I deleted the old WEB-INF and .war file which were created by goldspike, it worked very easily. I'm surprised and tempted to replace the existing jboss install with glassfish, provided it has similar throughput. The footprint is definitely smaller and it is much easier.
You can find more about using glassfish with jruby at the jruby wiki.