Hello,
Why not Migrate the SEPM to 12.1?
Please Understand, the SEP 11 and SEP 12.1 are 2 different products with different Architecture.
Basically, when it comes to communication, it would communicate and get managed.
However, when it comes to definition content updates, that would not happen.
As SEPM 11.x would only download the content meant for SEP 11 and not for SEP 12.1.
In reference to policies, SEP 12.1 policies are lot different than SEP 11.
So, I would say it is not adviseable to have the SEP 12.1 Clients managed by SEPM 11.x
Reference: https://www-secure.symantec.com/connect/forums/does-sep-121-client-reports-sepm-v11
Hope that answers!!