Taking to biologists it’s typically a whitetail buck breeding a Muley doe.

I ran across a herd of mule deer does in west Texas that had a single WT doe that hung with them. Apparently she had for years.

I was always curious if a muley buck ever bred her successfully?

not sure about the whitetail and exotic crosses, but had a landowner tell me I killed a red deer hind that was a cross with another exotic on the ranch