My 2002 Winnie has the Xfer switch in the power junction box in the electrical bay where the 50A cable is stored.
I've started my genset while connected to 50A shore power once a month and run it for 2 hours before shutting down to exercise it since I bought the rig in February of this year. The circuitry does such a good job, I can't even tell when the genset takes over, or drops out. Totally silent, no blinking of lights, neither the TV or computer show any evidence of the change over.
So at least with mine, I think it's perfectly safe to run the genset when on shore power. And to shut it down as well. JMO!