A friend of mine raised Belties for awhile, and she was always told if the bull wasn't a belted, the next generation could possibly lose the belt. She had quite a few with an 'incomplete" belt or no belt when bred with a non-Beltie bull.
Hi We have line here of belted galaway x friesian steers. All are black and have kept their full belt, I expect you would have similar results with an angus/galaway X.