So the other day the locknut/spacers on my rear hub snapped when i was tightning the lockbolts down, and i got some used spacers that kind of fit, but are a bit wider than the last set. now, when i put on my rear wheel, the hub pushes the dropouts apart maybe a half centimeter or so. is this terrible to ride/use the bike in this condition? i just couldn't find the right kind of spacers to keep the same exact spacing that it had before.
Soma DoubleCross, Surly Steamroller, various others
Use some freakin' junk washers, get that thing the right size. Like its been said, you won't hurt anything by riding it that way, but if it were me it would drive me nuts. The more accurately you have your wheel spaced out, the better your bike will track and the better your chainline will be.
Or just buy a spacer, they cost chump change.