I guess leaving boots outside would not be a good idea in a city that had dirty air. Coal dust, wood and other smoke, pollen etc., could coat the boot. To some extant, they might wipe or buff off, but I've seen buildings in cities like Philadelphia and Pittsburgh that looked so dirty that I'm not sure anything short of demolition would remove the dirt.
A major "active ingredient" of smog is ozone... but maybe not enough to help. And I'd bet if there were enough ozone to sterilize bacteria and fungi associated with stink, there is also enough to be unhealthy to people - especially if you are asthmatic, but maybe otherwise too.
Are modern hockey skates constructed from leather or are they mostly synthetic?
Almost all modern hockey boots are synthetic. Very few modern hockey skaters (I think a very small fraction of the goalies) use leather boots.
AFAICT, leather is just dried out skin (usually cow skin), chemically treated ("tanned") to resist bacteria, fungi, worms, maggots, and other living things - though apparently not completely enough, if there is stink. Live skin is affected by UV, so I'm sure leather can be damaged by UV too. (Of course, UV covers a wide range of wavelengths - don't know what the shoe sanitizers use.) I'm sure ozone will react a bit with the finish on the outside of the boots too. But if you have this problem, you have to decide what matters more - stink and decomposition, or occasional minor damage from de-stinking operations.
Better yet, always wipe the boots dry, and let them dry and be stored in the open air (
assuming your home isn't too humid), not in a locker, bag, car trunk, Zucca, etc. The boots will probably last longer too. I've never knowingly had all that much trouble with boot stink not even on my prior 12 year old Klingbeils - but my feet don't sweat much, I am careful to let boots dry in the open, and my sense of smell isn't that great, so maybe I just don't know they stink.
I suspect most of the smell is from the inside of the boots, because that's what gets most wet, though if you keep the boots in a locker, etc., moisture will to some extant spread everywhere. So if you really care about color, you could cover the viewable outside of the boots with masking tape during treatment. Who cares if the insides discolor?
Your skate shop would be very happy to replace your boots every time they start to stink, for a "modest" fee!
Think of them as disposable?