Since we're on it, was there *not* one episode of the show where the
announcer on the radio said, "This is KGU Honolulu"?

I keep thinking it was uttered on an episode, but I'm not sure....maybe
it
was in a dream of mine....I just thought it unusual to hear *actual*
calls &
COL on a fictional show....

Did this *really* happen?

Could be. I haven't watched a GI episode in many years....

Not in the first season, for sure.
I purchased the first season on DVD and I've seen them all with no legal ID
on the radio.
Yes, I admit that bought the first season... those black & white episodes
with the opening theme that calls the professor & Mary Ann "and the rest".
They went to color in year 2 and changed the theme to give credit to Russ &
Dawn.