Harmonix Creative Director Josh Randall confirmed to us today that we should think of the Rock Band platform and The Beatles: Rock Band as two totally separate entities. Meaning, that The Beatles: Rock Band tracks and DLC will not be playable with any other Rock Band songs and vice versa.
So, only owners of The Beatles: Rock Band will be able to download the Abbey Road album when it's released as DLC later. There will also be no export feature for The Beatles: Rock Band into Rock Band. It's really a shame and one we hope that some licensing agreement in the future can fix.