Personally, I think it'd be disappointing if they shoehorned Michael Myers into a Season of the Witch house more than as a cameo or final scare. The team does such a tremendous job at paying homage to the IP properties when they use them that I think it'd be weird for them to produce a house based on a cult classic like Season of the Witch and it to be a mish mash that isn't actually the property solely to include the iconic killer that's been a featured IP several times already.
At that point, either do a different Halloween film you can access or have Myers in his own unique tale, don't potentially muddle Season of the Witch just for Myers' sake. I agree most with the idea that this likely isn't even going to be that featured of a house so it's not as if they're banking on Myers to sell tickets. Given the circumstances it's quite the opposite so if they want to throw a bone to something as niche and cult as H3, this would be a great year to do it.
It seems like a weird component to bring up that people would see the Halloween 3 title, not know anything about the title, expect Michael Myers and be that upset that he's not there that it'd be any kind of problem past the most basic "shrug, where was Michael Myers at?". Not to mention if they do as good a job as they usually do with an IP, story and scares will work well enough that level of event goers will still have fun to the point where it won't matter anyway. Make the house good, have your Myers cameo or final scare and it won't matter that MM isn't the star of a Halloween house. They'll pick up on the idea that the story doesn't involve him and maybe even look the movie up after the fact. If you want to be ultra safe, just call it Season of the Witch or Halloween: Season of the Witch.
This is all moot anyway, with the amount of time the house needs to devote to Tom Atkins, there won't be any left for Michael Myers.