I don't really see what Santorum has to do with any of this (other than the BRTD/Keystone Phil circlejerk). Pennsylvania residency requirements are rather relaxed, whereas Louisiana's are quite draconian. If Santorum was in Louisiana, he might not be able to run either.
It is also assumed that representatives and congressmen are going to spend the majority of their time in Washington, and that many are going to maintain a second residence in Virginia or Maryland, that given housing costs is going to be more expensive than their home back in their home state.
Residency for Congress only has to be on election day, and it will be judged by the other members of Congress. And they aren't going to outlaw something that most of them are doing anyhow.
Breaux was Edwin Edwards' assistant from the time he was 24, and then was elected to Congress at 28 when Edwards became governor. I'd guess that any home he had in Louisiana was more to establish residence than a place to live in. After leaving the Senate he registered to vote in Maryland.
Louisiana requires its governors to have been resident in Louisiana for a year before election. No one would have to challenge his residency until he actually filed. It's not going to help if he has to explain who he voted for Senator last November. If he picked up a Louisiana driver's license and registered to vote in February 2007, it's going to look fake.
Of course, politically it might have helped him. Louisiana admires corrupt politicians.