That is a very subjective decision to make and hints that the whole issue is one of semantics. Many, many (but certainly not all) of the "nondenominational Christians" are the most Protestant congregations out there. In fact many of those churches were formed by orthodox Protestants fleeing their now liberal Mainline denominations for a completely Orthodox, bible based, nondenominational Church. They are congregationalists and from an ecclessiastical standpoint are almost identical to Baptist churches.
As long as this fleeing is to a Christian group, its ok — and I’ll be generous to also include the Oneness in my opinion. But it would be horrible for folks to leave to follow Benny Hinn for instance