I mountain bike a decent amount and have never used mine for deer hunting. Run and gun turkey hunting I use it all the time, it's great for that.
For deer I have a few hangups as I would use it, these are just some of the things I think about with it. Biggest is coming up with a system to haul my bow that I feel comfortable is still going to get through brush on singletrack. Also worry about dumping it, as anyone who has mountain biked enough knows you will do from time to time, and getting hurt worse because of carrying a pack full of sticks on my back. And/or destroying my bow which would wreck a good part of my season since I've never seen the need to carry an up to date backup bow. That setup in the kiui ad above looks pretty slick, but I'd still worry about dumping my rig and wrecking my bow. Would have to stay on much milder roads than I have in mind for that to work. Thought about a trailer and PIA factor there outweighs benefits as I see it and would also restrict where I could get to. Maybe 10% of my current spots are even candidates where I could materially cut time from my "commute" to the stand.