Hey Altron, Don't Touch Anything I own.
It seems that you think that if someone doesn't expressly say you can't use something, then you can. Despite the fact that it's locked up.
Y'know. I let my brother in law borrow my car if he needs it. But that doesn't give him permission to take it any old time he wants. That they locked the snowblower up and didn't give you the key tells me that while they don't mind you using it when they're there, they don't want you using it when they're not there to monitor it. Maybe they don't want you using their snowblower to go clear everyone's driveway and make a pocketful of cash?
BTW, if you had the keys to their house, why didn't you just go inside and get the key to the gate? If they didn't leave it, it's pretty clear they didn't want you to have it.