I have deployed Grails 1.3 apps to WebSphere in the past and there were a few hiccups, but nothing that couldn't be fixed (http://grails.org/Deployment#Websphere 6.1). That was a long time ago and I can't think of any reason why it wouldn't work on the latest WebSphere 8.
The only thing you could run into is if WebSphere includes a duplicate Jar but different version of something that's packaged with Grails. I always configured WebSphere to be PARENT_LAST anyway with any Spring app to avoid those classloader issues. PARENT_LAST allows an application classloader to override and provide its own version of a class that exists in the parent classloader.
I'd say give it a try and see if you run into any problems. If you do, just post the exceptions / deployment errors to the mailing list so we can help get them resolved.
I've tested some simple Grails 2.0 apps on WAS 8 . I didn't notice
It's required to set "-Xverify:none" in "Application servers > server >
Process Definition > Java Virtual Machine" -> "Generic JVM
arguments". (The same applies to WAS7, for WAS6.1 there are
more settings to tweak.)
Without this setting the application startup is extremely slow and
the JVM crashes quite often.
We created several POCs and deployed it to websphere 8 with default setting. (AIX, IHS, Webshpere)
1) It works correctly but very slow.
2) Cluster environment does not work. Assets are missing from one or the other server. At this point we know we know that it has something to do with Resources plugin. Removing Resources plugin make it work.