Each state bar will have their own criteria generally called a moral character application. Here is a link to the California Bar preliminary questions http://admissions.calbar.ca.gov/Requirements/Forms.aspx
if you declare bankruptcy it comes up, but missing a credit card payment is probably not going to prevent you from going to law school.
As for individual law schools make an LSAC account and look at the various applications. Each school has a slightly different form and one might ask about Credit, but back when I was applying to law schools I never remember it coming up.
If you have a judgment against you or bankruptcy they will ask, but like everything in the law just disclose. Having bad credit doesn't make you immoral etc, but lying about it would.
You should call the state bars and schools you are interested in directly to see what they say, but from my experience I have no recollection of any type of credit score being an issue during the law school application process or going through the California Bar background check.