Dunno what Lex's blood type would be, probably something normal. I wonder what Clark Kent's blood type is officially? How does a normal human doctor check up on an invulnerable alien without getting suspicious? I know Clark has a dentist, who loves seeing him because Clark has the best set of teeth and always brushes and flosses. (I bet Jaime Reyes will eventually become the dentist to the superhero crowd when he graduates.)
I would think that if Batman knew, he would tell Clark, and Clark would tell Kon. Then again, Clark didn't tell Kon his secret ID for years, Kon found out accidentally, and Clark only told him so Kon would call Lois for him. (That was during Sins of Youth, for those who don't know.) So there's a history of Clark and Kon not talking about Important Things.