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.