In NSX-MH (multi hypervisor edition), the controllers use openflow to talk to OVS.
That said, I assume you're referring to NSX-V (the vSphere edition) - its what most people use unless you are a large service provider. It doesn't use OpenFlow to talk to the VDSes, just native vmware APIs. Some might argue that it sorta uses Openflow for hardware VTEPs. It uses OVSDB to talk to supported hardware switches (arista, brocade, cumulus, etc) - but I would say hardware VTEPs are only involved in maybe 25% of the NSX deployments I've worked on.