Dontomasso wrote:

It odd too that Tom thought he could tell her that Michael was "all right," but nothing more. If Kay had been subpoenaed and was forced to testify she would have had to tell the court that Tom Hagen admitted he knew that Michael was "all right."
Such an admission against interest would be circumstantial evidence to show Tom did know where Michael was, or at least knew hw to contact someone who did.

that would never fly in a court of law....
saying that someone is alright. and saying you know where someone is, are two differen't things.
example:
say your dog is missing. I am not going to tell you "oh your dog is probable lying in the road dead! or has been kidnapped!" I would tell you "don't worry your dog is alright".
human nature.
Hagen handeled it perfectly.