I may be being paranoid...

because you would be axle gridnding the lock that wasnt connecting the 2 bikes together. if you lock your bikes to someones, then to free them you have to grind that lock, not the one securing one to the fence...

No, the point of the lock would be if anyone asks what the hell you are doing, you claim to be grinding away the lock holding both bikes together, but in reality you are grinding the locks holding the bike you want to steal. That way, you can stick around a bike rack with an angle grinder and have a 'legit' reason to do so, meaning you could angle grind a bike away in the plain light of day as long as no one was paying too much attention.