Most of the Grails commands are replicated through Maven dedicated goals.
I've used this plugin myself to easily integrate a Grails app in my continuous integration server of choice, and to be able to depend upon existing in-house libraries stored in an Enterprise Maven repository.
Maven Tools for Grails
Graeme Rocher responded to your post by detailing some of the reasons why the Grails team didn't use Maven:
http://graemerocher.blogspot.com/2008/01/why-grails-doesnt-use-maven.html
And regarding your last question, there's already a Maven plugin that sits on top of Grails that you can use:
http://forge.octo.com/maven/sites/mtg/
Most of the Grails commands are replicated through Maven dedicated goals.
I've used this plugin myself to easily integrate a Grails app in my continuous integration server of choice, and to be able to depend upon existing in-house libraries stored in an Enterprise Maven repository.