Okay, on the surface this sounds like a wonderful story, and I certainly hope it is true, but your family definitely needs some evidence that this person is on the up-and-up. Unless at very least some family member knew about the pregnancy, you, and especially his siblings, probably should insist on DNA evidence and/or should try to track down the birth and adoption records independently. A con man could be trying to finagle his way into your homes or hoping to get an inheritance. It never hurts to be cautious. Possibly the easiest thing to check out is proof that he really was a neurosurgeon. Consult the medical board in the state where he says he practiced. Also check about that bar exam. I hate to be negative, but he seems a little too good to be true! If he is telling the truth, he should not mind at all that people want verification. If he evades any questions or seems nervous or vague, you must go with extreme caution.
If he knew the parents' names he could surely have accomplished the goal of finding you 10-15 years ago, it seems to me. Also, most certainly if you, as a female relative, customarily use a name that you acquired by marriage, you have to wonder why he didn't first find and contact one of the male relatives.
I believe that in most places for many years now, before a divorce is granted there is a waiting period of several months. There are questions about the possibility of a pregnancy. After the waiting period both parties have to appear and sign papers. Divorce laws are written this way in an effort to protect the interest of children, including those not yet born. It probably would not have been that easy for your aunt to have a baby that her ex didn't know about, and then to give the baby up, the rights of both parents have to be severed. If a child is conceived during a marriage it is considered by law to be the father's child, whether this is true biologically or not. I can't begin to guess if this would have been true in every state 60 some years ago, but it seems like a good bet that it was probably true in most of them. Best wishes!