I first heard the terms "gate house" and "head house" from PMDL employees after the NW/DL merger. I've seen the terms used in plans for the build-out of JFKIAT (referencing the expansion of the terminal head house -- check-in, security, baggage claim, etc.) and frequently hear DL employees refer to the "gate house" areas.

Airport folks I know (around the country) usually refer to gate areas as "hold rooms" -- but if you say "gate area" no one skips a beat.