I was thinking about the conversation between Snape and Moody (who was really Crouch) in the Egg and the Eye, when it appears Crouch/Moody knows exactly the situation Snape is in (the whole bit about Dumbledore trusting Snape, and some "spots" that never come off...)

But you're right, Crouch was Kissed at the end of the book, wasn't he? He never went back to Voldemort (I love when I forget big stuff like this!) Voldemort knew of Crouch's plan and I guess they could have communicated throughout that year - but we don't know, which leaves the big question of what Voldemort knows about Snape still unanswered.