It's a little confusing, but after a 3 hour TSupport call this AM, I'm starting to get a handle on what BES 10.1 is & isn't.
BES 10.1 will only support BB10 devices & Playbooks natively, and Apple & Android devices via ActiveSync. Legacy BBOS 7 and older devices will still need the legacy BES 5.x server. You can, however, 'connect' the BES 5 to the BES 10.1 server and get an overall view and do basic user administration via BES 10.1 Management Studio.
Apparently if the server you are currently running 5.x on has the specs to run BES 10.1, it is possible to run both on the same server. In my case, the BES 5.0.4 server is on Server 2003 32bit, so it wasn't an option for me. I created a Server 2008 R2 64bit VM to host the BES 10.1 server. My exchange setup is Ex2k3 Enterprise on Server 2003.