Bounty hunters, in most states, aren't court officers, they're bondsmen employees. How can we dictate to other countries how to handle their laws? Very few countries have legalized bounty hunting, as far as their concerned it's kidnapping. And remember bounty hunting laws vary drastically from state to state, a bounty hunter licensed in one state (assuming that state has a licensing procedure) might not be allowed to operate in a different state (again depending on that stat's laws). Suddenly declaring they can operate internationally with complete disregard to local laws when they can't even operate throughout the US that way would never stand.
Everything aside, what Dog did was good for everyone. He helped protect Mexican women from a serial rapist and brought justice (not to mention peace of mind) to the American women Luster raped and beat.
I've a gut feeling this is about money and not so much about any laws broken. I don't have a lot of confidence in Mexico being honorable about their laws being broken. Maybe I'm sterotyping.