In theory, yes, it's doable. Grails plays well with Spring & Hibernate.
I don't have a lot of experience with Grails, and I certainly haven't augmented an existing, so I don't know how _quick_ it would be. In the vein of Rails, Grails prefers convention over configuration, but definitely _allows_ configuration for legacy/non-standard situations.
I don't know of any tutorials in this aspect. If you have specific questions, you might try the main site and look for mailing lists and/or blogs. http://grails.codehaus.org/