Have to say, if I had to pick a guy in the Buffyverse who makes a living being non-magical, it wouldn't be the werewolf, it would be either Xander or Riley.
Giles might be a runner up since though he has access to a whole heap MORE magic than most, he consciously doesn't use it, despite the fact he could.
Oz, on the other hand, is magical by his very nature as a werewolf, the fact he can control it, and the amount of magic he has on him may depend on his emotions controlling the amount of werewolfness in him, seems very contrived as an explanation.