I watched all my recordings off my old disconnected 522 (I know, it is not a 622) when I upgraded to a 722. No problem. It will of course appear to be hung up on the "acquiring satellite" screen, but you can get to the menu to bring up your recordings anyway. IIRC, I used the "menu" button and then picked my recordings from there, but DVR+DVR should work as well, as others have mentioned.
As jwfgeol said, just unhook your 622 NOW, and see if you can access the recordings as a test. This will give you more confirmation than any number of posts here ever could. Nothing beats personal experience.