Thank you for your feature request in JIRA. Actual for this is https://jira.jboss.org/jira/browse/JBIDE-6117.
First t ask I can see here is enabling seam-gen to generate groovy code instead of java. Now JBoss Tools uses seam-gen resources to generate all artifacts in IDE:
1. XHTML pages are generated using seam-gen/view seam folder templates and shey should stay the same for Groovy;
2. java sources generated using seam-gen/src folder templates and thus groovy templates should be implemented;
3. test sources generated using seam-gen/test folder templates and also needs templates in groovy.