An open 30 with 37's will last a lot longer then a 30 with a locker.
Once you bind a 37" tire with a locker something will have to give.
Stock axles will break first, up grade the axles and u-joints and you will move your weak point to the small ring and pinion. Not only are you looking at binding a tire but the extra weight of the wheel will put more stress on your drive train and all your suspension and steering parts too. Getting the tire to fit under is only one issue, you must remember all the other parts that are not built up for that kind of strain.
I ran 37's on a 30 for a few years, never with stock axle shafts, but I broke a lot of parts too.