That's a good question! If left untreated, I'm sure that it could, since a lot of this spalting seems to be mycorrhizae in the wood. I'm going to try a couple different types of water/weatherproofing treatments on the siding when I build my new chicken coop, to get a better idea of how viable this will be (before I go putting it on my house!) I do know that the spalted maple I've seen used for guitar bodies and other woodworking style projects seems no different from any other maple, in terms of durability, and I've never seen any of it begin to grow after being treated.
I'll do a post about this in the future, when I have more data. I'll tag you in it, if I remember!