Dumbledore never explicitly made a deal of what potential he thought Tom Riddle at school was capable of in terms of evilness. He was very observant of course and he made sure Riddle knew someone was watching him. But Voldemort had first hand experience and so he thinks that Dumbledore is capable being fooled. He didn't understand what Dumbledore told him of not being able to make him frighten of a burning wardrobe. He'd always relished in the idea that he had bested Dumbledore.
There is no way Voldemort would believe that Dumbledore would hire Snape as a teacher, it doesn't make sense.