There's no way that a Subaru mechanic is going to be able to bill Saab for the warranty work. It doesn't matter who's parts are under the hood. It all comes down to who's badge is on it. Typically in GM a dealer from one division is cleared to bill another division for warranty work done (ex. Chevy and Pontiac), but if you go to a Saab / Cadillac / Hummer dealer they won't let a Cadillac mechanic even change your oil...even on a Sabaru.