Here is some insight as to a possible reason that Generac used DC Coils. This is about the most definitive thing that I have found. There are other functional differences, but they wouldn’t really be applicable.
To be clear, the integration of My Onan transfer switch to control both a Generac switch and Generac generator has benn complete and works well. The generator supplies both my house and workshop through separate switches in the event of a utility failure. It was my research of the Generac switch that prompted the question, but it was out of curiosity, everything was already working as I wished.
This is from Sciencing.com-
AC solenoids can run the risk of burning out if they malfunction and remain stuck in the open (full-current) position for too long. The current that runs through an AC solenoid starts with a first rush of extremely strong current, then drops to a lower, normal level. If the solenoid stays open too long and receives too much of this first wave of maximum current, it can permanently damage the device. By contrast, DC solenoids experience no alteration in currents and do not run the risk of being damaged by the current.