There are rules against playing for more then one team at the same USTA level. Please provide more details! I want to see this person's USTA record? Did they play under different USTA Numbers?
There are sectional rules, state rules and local rules that govern this. Each can be more restrictive. I was under the impression that the player (in SC) had to reside in SC. But I may be wrong. All the applicable rules are posted in the various websites.