Your comments mirror my thoughts but the unit takes so much less space in the service position.I would say in general engines probably shouldn't be stored in abnormal positions. If it has gas (which hopefully it doesn't) it could leak everywhere. Oil can get up into the cylinder or possibly the carb depending on how it is leaning. You would probably be safe if you drain most of the oil out too, but then you have to make sure you remember to fill it before starting it.
Also you front gearbox should be sealed all the way around, but turning it on end might cause oil to leak out of it from a bad seal that isn't normally visible.
I can't think of any other problems, but I don't know a whole lot and what I said above might not even be true.