I flew recently with one captain who insisted it should be "Gee-Es" because "glideslope" is reserved for calling out of stabilization criteria. His reasoning being, that when he hears "Glideslope", one cannot be sure whether it's mode annunciation or a callout that something is wrong with the glideslope.
I have to admit, there is some merit to his thinking, but as with many other things in aviation - I cannot think of any situation when there could be any confusion regarding those two events, even more so one that would affect safety at all.