Wow, that is completely bogus! Didn't the DEC guy see the damage to the other car? What about the drive of the other car, did he not corroborate your story of why you dispatched the deer?
I hope the judge isn't as anal as the guy writing the ticket, and that you got the name and address of the party who hit the deer in case you need a witness.
Good luck, and it will make me think twice about what to do if the situation ever arises!