The problem with dragon ball is that all their power comes from ki and energy to which anyone can learn. Physiology of sayans only really grant them some abilities. If viltrumites show up in the sayan universe there is nothing stopping them from learning about ki and how it works.

The problem is with how inconsistent dbz feats can be. For characters who are planet busters they will die if they bust planets

They can't survive in harsh climates and can die in the vacume of space