According to a recent blog post of Grails project lead Graeme Rocher, Grails is getting Maven support in the form of a plugin.

Currently, Grails uses Maven repositories for dependency resolution, but the build system of a Grails application uses Gant. For Grails 3.0 it is planned to establish Gradle as the build system of choice, as Gradle is getting more and more popular.

But as Maven is already widely used in the Java world, Graeme wants to provide Maven as an alternative build system.
There will be an initial plugin providing basic Maven support soon, which will be compatible with Grails 2.0.
A more refined integration will become available later, but it will probably requiere Grails 2.1.