This question already has an answer here:
Families like the Malfoys were more than willing to serve Lord Voldemort, whose father was a Muggle (not even a Muggle-born wizard).
In the books was there ever any indication that the Malfoys, or any of Voldemort's most loyal followers, were aware of his half-blood status?
I believe Voldemort went to great lengths to hide that information from others. I'm not even sure Snape was aware, though Dumbledore, Harry, Hermione, and Ron knew through their hunting of the Horcruxes.