When deploying OSPF in relation to a L3 MPLS VPN, the important thing to remember is that OSPF will form neighbor adjacency with the PE routers normally, whether it be P2P, broadcast, or NBMA.
All traditional requirements are valid for building this CE-PE neighbor relationship, including matching Area ID, hello/dead timers, MTU, authentication, etc. The nature of the MPLS removes all complexities of the backbone from customer view, and carries customer routes to each site via multi-protocol BGP.
The most important thing to remember about this PE-CE relationship is that the provider and customer must agree upon OSPF parameters to establish proper adjacency. Usually the service provider will provide specific direction.
Stuck-in-Active: Journal of an IT-Network Administrator 