Cal45,
I have pictures of a Jacob Dickert rifle with an 1829 dated silver coin inlayed on the wrist of the gun. The rifle is much earlier than 1829, so it probably wasn't put there by Dickert, but by some owner that thought it would look cool. It's attached with a single nail right through the center of the coin, the same way that Dickert would have attached the original inlay.
I haven't seen a coin on the cheek, but see no problem with putting one there.
John