I have dressed that way for Halloween as it was a last minute request to walk 12 kids but I had to be in a costume. My landlady was my size so worked well but I was scared as many kids I overheard saying wow mom that woman has a beard!
So yes I would let them it is just a costume no different then a devil costume or a wrestler to me.
Considering these are serious issues for people out there I wouldn't do it or if I had children I wouldn't let them do it. Imagine knocking the door of a cross dresser or transvestite. There are way too many costumes out there to pick that.
I'm not sure why knocking at the door of a crossdresser or any other kind of sexual identity-different person, with a kid crossdressing, would be weird or wrong - in fact some of them might think it's cute or be impressed with the parent being open minded and not threatened by such things. If my kid asked to do it, I'd probably let them after having a brief talk with them to make sure, but I of course wouldn't suggest it.