I see WT's and MD often within feet of each when feeding in ag fields. They even bed close to each other near field edges. One thing I have noticed is when they get spooked, they often separate even if they are right amongst each other when spooked. Each species seems to select a different escape path.
A couple years ago, I watched a decent-sized WT buck with an in-heat WT doe. Mule deer bucks and does were all around them feeding, bedded, sparring, etc... A couple small WT bucks were also hovering in the vicinity trying to get in on the hot doe action. The little WT bucks were way more persistent and aggressive when trying to get close to the doe.
Whenever a mule deer buck wandered to close to his doe, usually 20 yards or less, the WT buck would run them off. I'm pretty sure the MD bucks could smell something curious about the WT doe, but didn't have any fighting desire to take on the WT buck. Most of the MD bucks outweighed and out-antlered the whitetail buck by a fair margin, but that didn't stop him from giving them hell. He run them off a 100 yards or so and go back to his doe.
