Are you asking about it benefiting you getting a license in the US? Some of the online masters accept foreign dentists but they do not help you get licensed. It is more for continuous education purposes and can also help with your resume when you apply for DDS programs. At the end you will need to check with each Masters program coordinator separately and not try to generalize. Also, are you talking about a specific online program? Which one? I may have more info depending on the program you are interested in.
Good luck!