Of course you can use our NPC voices as simply a starting off point for your OWN voice acting. I find when an encounter then progresses elsewhere and I take over with my own acting, it really helps to set the personality of the NPC, when the Players can actually hear their voice for real. Also: Chris Perkins, Mike Mearls, James Jacobs or Matt Mercer DMing at your table? How is that not VERY cool!?!
I don't want to use your NPC voices, I am much too brilliant an actor for that