I'm certainly not a authority on elk-deer co habitation but will offer my opinion more geared to WT-Mule deer intermingling.
All of my elk-deer experience comes from high alpine hunting in western Ab. 30 yrs. ago, none from lower parkland areas. It certainly wasn't uncommon to see elk & mule deer feeding in the same high mountain meadow, sometimes within a couple hundred yards of each other and didn't seem to matter what ### they were. Back then I have no recollection of ever seeing a W/T in the foothills or high country, just Mules but I've had local hunters that still hunt the high country tell me that seeing a W/T above timber line is not uncommon now. Grizz. can you confirm this or not?
Deer intermingling in my home hunting area is another story. My hunting area is about 8 miles square and over 45 yrs of hunting this area (all farmland with some easy access to most areas) I have become very acquainted with the deer habits locally . I worked/farmed this area year round for a # of years so spotting was a daily thing and hunting happened every day the Nov season was open for all those years. I can say without a doubt that W/T and Mules do not enjoy the same neighborhoods. When I was younger and a lot more active at scouting & hunting I could pretty well tell you what kind of deer you would encounter on one side of a fence line or another with very little overlap. That doesn't mean that they don't change area's from one year to another...It seemed that the W/T were more dominant and when they moved into an area previously the domain of Mules that the mules would move on to another block inhabited by their brethren.
The thing that ended the W/T dominance in most area's was a sever winter die-off a few years ago. My own home 1/4 is a good example of this. For years the only deer we seen close to the buildings were W/T...then the first big die-off happened and I haven't seen a W/T within a mile of our place for 5 yrs., dozens of mules through out a year come thru the yard but not one W/T. Not many days a year I cant look out the windows of my house and not see 1 or a dozen deer within 30-50 yrds of the house. A week ago I had 8 Mule bucks within 50 yrds of my house, 4 were spikes or forks but 4 were fully mature 4x4 or 5x5 (brows), 3 in the 150-160 class and one definitely in the 170-180 size. The big one was back in the yard yesterday but unfortunately he has broken off on of his rear forks this past week so his "trophy ranking" has taken a severe hit. I have photo's of him & a buddy that I can text someone if they want to upload to the forum.