Hi Dwayne, and welcome to the BrickWood forums!
I just want to clarify before I respond to your question: by the “hearth bricks” do you mean the outer edge of the hearth? Or are you talking about the firebrick inside the oven?
If you are talking about the outside frame, then yes, absolutely. You can finish that as you like. I just saw a finished oven where the builder used granite to cover the rough brick surface and it looked beautiful.
If you are talking about the inside of the oven (which is where we consider the “hearth bricks” to live), then no, absolutely not. Different kind of brick and very different job. The firebrick must be your facing contact surface for the fire; any treatments or coatings will affect either the coatings themselves or the food you’re cooking.
I’m so pleased you’re at this point with your build, and looking forward to seeing that custom work, Dwayne!