Hi Keith,
OEM can be done on different levels. For example, all the Q-Acoustic drivers are designed in here in Essen with production in China, but with one of our engineers sitting in the factory, using Q-Acoustic tooling and jigs, glue and so on. That's a kind of extended workbench approach. OEM could also be a small change of an existing driver, as I made it ages ago myself with VIFA in Denmark. Or buying cheap crap drivers with your logo on
All depends...
There are still some companies doing drivers from scratch: B&W, Dynaudio, Focal, Magico, Vivid, all the IAG brands like Wharfdale, MISSION, ATC, Quad and Castle, some Spendor and Harbeth - I'm sure, there are a lot more
ATB KH