The designs for the VF-4 from those video games would still belong to BW (Macross name on game, yadda, yadda, yadda) whether Kawamori did them or not. But the simple answer is, unless HG comes up with their own transformation of the VF-X-4, they really can't use any design BW created. Also, IIRC, the designs for those games was for the VF-4, not the VF-X-4. And since they have no claim on the VF-4, it's not going to be a big problem.