I seriously doubt if the base plate was factory installed. Maybe dealer installed, but not factory. I owned a 2000 and a 2003 model of those and none came with base plates. It is a fairly expensive accessory for a very limited audience, and no, it is not universal. There are, however, adapters that can make Roadmaster brackets work with Blue Ox or vice versa. Demco has adapters that connect to either Blue Ox or Roadmaster base plates as well.
If you can post a photo of the base plate connector, we can probably identify it.