Good idea in theory, but I don't know if it would work in practice. You could always give it a try and test it on a few of your own galleries before letting others use the service. But for $15 you can register a domain with Directnic.com and have it forward to any page you want. Even a gallery URL like
http://mydomain.com/gallery/page.html will redirect without problems. I think even the most avid freehost users can afford $15/year.