you might have looked at my first comparison of extval and the seam 2.x integration of hibernate validator . some of you were interested in a seam support of extval to get the best of both frameworks.
i've tested extval with seam and it worked quite well. to use extval also with richfaces the generic-support module of extval is required. some weeks ago the test with myfaces core was successful. there is just an issue with the combination of (richfaces + extval + mojarra). if you would like to use this combination, feel free to look into the issue and provide some details and/or a patch to fix it.
furthermore, it's possible to use both solutions in parallel.