Do you mean, will you incur any legal penalty for doing so, or just be violating their ToS? I don't believe so but haven't researched it in depth. It'd be tricky to sue because the right of publicity is generally treated as a property interest and you wouldn't necessarily be able to show any economic loss. I'm not an attorney though.

In practical terms, I'm sure it's against the ToS but really the service providers have no way of knowing unless the person has already submitted their DNA and your submission raises a red flag, thus cutting you off from the information you desire. This is interesting from a game-theoretic standpoint in that it might be more secure to give your information to every website and then be the designated owner, but it probably wouldn't shield you from law enforcement getting the same information via subpoena. It's an uphill argument to say that a general right of privacy weighs heavier than the unsolved cases of 10 murders and 50 rapes, a record which will probably be broken again in future.

I don't think DNA testing companies have much incentive to screen potential customers since each person can only submit DNA once without raising another red flag.