If there is a need to close the doors/ramp, get a crewmember on, disconnect the grounding cable, get personnel clear so as not to injure them, then, there is no reason I can think of to not have engine(s) at idle during the refuel.
And, since the people outside may not be able to be on the ICS, engines to operating RPM serves as a good attention getter to alert of somthing not normal happening.
Lastly, one engine or two, I can't see that the time necessary to bring engine(s) to operating RPM is a common save-the-day piece of time.
Hell, It'll take me that long to wake up from my nap!