As Ronen said, there are no specific provisions in the MDR for OBL/OEM. In fact there were never any in the MDD.
As a word of caution, in the past, OBL used to be a quick route to market, you could request some documents from the OEM, sign a Technical agreement, promise to collect and report complaints and pretty much forget about it.
Over the last 5 years of so, this lax attitude has progressively tightened. NB's started requesting more documentation; you must now stay on top of the documentation and maintain it (don't let it gather dust).
In the last year or so, I've frequently heard people say that OBL/virtual manufacture is dead. While I don't necessarily agree, it is certainly the case that the expectation is now that you are fully a manufacturer and must act as one.
In this vain, with regards to managing your OEM; you should manage them as you would any other supplier, however that may be. I would strongly recommend auditing them. You must be on top of document control, don't let your documentation gather dust, make sure they inform you of changes. It is a delicate relationship as they view themselves as the owner of the product/design, however while this may be true and accepted in the past, the regulatory authorities now view you as responsible and therefore in control.
