I am hoping he is not related to anyone. vivian is a schemer, & while he possibly could be her son, it would be just like her to claim Stefano as father, and manufacture a "DNA report" to verify.
It is too bad neither Abby nor Chad know of Andre's treachery, and unless Viv spills the beans, they never will. Stefan knows tho.
However, I do prefer that Stefan is not related to either one, that Viv found him somewhere, got him to agree to everything.....even perhaps the claim he was formerly Sam Maitland. (See, Sam was a corporate raider, who already had made millions.....why would he agree to change his name, to go after the DiMera fortune? Iffy thing, even with Andre's help. He did not need Viv, Andre, or anyone else to do it.
Could Sam Maitland actually be hospitalized somewhere, or held prisoner, thought to be on safari and lost in the jungles of Africa? So Viv gets some guy to take his place? Really, have we actually seen him conducting any business? O.K. take that back, we never see any one doing that, just talking on the phone to Mr. Shin. LOLOL