Judging from the list of features that will be included in NetBeans 6.5, Groovy and Grails will be officially supported by the NB team. From the wiki text, Groovy and Grails will be first-class citizen in NB65 with features that will include:
- Editor support (code completion, color highlights, etc)
- Two-way Java / Groovy class integration
- Seamless Grail project support (support for all Grails artifacts and commands)
- Jetty integration for development-time deployment/testing.

It remains to be seen if NB65 Groovy support will be as comprehensive as IntelliJ which currently has the most extensive support for Groovy / Grails development.

For more, go to:
http://wiki.netbeans.org/NewAndNoteWorthyMilestone1NB65#section-NewAndNoteWorthyMilestone1NB65-Groovy