It's not ideal or even supported but I've done this in the past and it does work. I even got AV defs to pull down on the newer clients from the older SEPM.
But Symantec will tell you not to do this (obviously) but I've had it working.
These KB articles should explain somewhat
https://www.symantec.com/business/support/index?page=content&id=TECH131660
https://www.symantec.com/business/support/index?page=content&id=TECH131718
I believe the schema did change in RU2 so that would be where you would see issues. Functionality wise you probably won't see anything.