Can SEP 12.x manage legacy SEP 11 and SEP 12.0 clients?
The answer is YES
https://www-secure.symantec.com/connect/forums/sepm-12x-managing-sep11-clients#comment-5530271
Yes, SEPM 12.1 (currently in beta) can manage SEP11 clients.
The same goes with SEP 12.0 SBE legacy clients: I have recently made some tests with migration from SBE to SEP12 beta, with largely positive effects.