I guess they could drive to Mexico and open up a PO box there,,, Hypothetically speaking am I on the right track?
They do not confirm or check your address, unless using credit cards for deposits.
They do not IP address check either, so you can log in from the states using your normal internet.
Therefore, you could open an account with a non-us address, fund the account, using sportsbook transfers which are free, with most books including: matchbook, Olympic, 5dimes, BetJM, Grande, etc.
And you could use the account perfectly.