To backup sharepoint from DPM 2012 you willl first have to install DPM agent. Then run %program files%\Microsoft Data Protection Manager\DPM\Bin\
ConfigureSharepoint.exe -EnableSharepointProtection
When asked fore WSSCmdletsWrapper user enter your farm administrator.
If you get an error :
Then the user you have logged on to the server with does not have the right permissions on the SQL instance.