I was able to use a 135mm wheel with my 130mm frame.
It seems some shimano hubs have a 5mm spacer so it could be used with either sized frame, but the skewer and axle are too long for a 130mm frame.
Instead of getting a new axle and skewer, I just put the spacer on the outside and redished the wheel. I find this more desirable than spreading out the stays cause that gets annoying when you want to remove the wheel often
Is there any reason why this isn't ok to ride? The only thing I could think of is that there is slightly less surface area holding the wheel in place on the side with the spacer, but as long as it's torqued down good, it's not going anywhere in the vertical drop out anyways..