I have altered user.module to accept only a-z|0-9 plus hyphens. Will this be an issue?

I have altered the function user_validate_name part of user.module so now it's more like a whitelist instead of the default blacklist (which was never complete and let in a whole array of left field characters).

so, on my site at the moment, I only accept letters, numbers and hyphens.

what if someone with a Open ID username outside these restrictions tries to sign up? Is that going to cause a problem?