Here is another Frequently asked question on SCCM :
Proxy management Point and A Management Point : Well Both are Single point of Contacts for the Client . With primary Site the clients being assigned to the primary will report to Management Point at Primary site . With Secondary site , Clients assigned to it will report for proxy management Point ( Which is Management point at Secondary Site )
So in a nutshell A proxy management point is a management point but it is present on Secondary Site . Rest All is same .