No relation to you MR but I've found that most TM reps don't have a clue and also that when they don't have a clue they feel free to make up crap rather than seem dumb.
The official info on the update is here:
T-Mobile Support Community: Software upgrade to Android 2.3.4 (Gingerbread) - T-Mobile G2
I can also say that it does not affect tethering and also that it adds/changes other things not mentioned. For me at least it seems to have solved the issue of photos not showing up in the Gallery. It also improved the Market's ability to handle more than one Google account on the phone (i.e. the Market update notifications are now specific to each account).
Over-all I think it's a big improvement and corrects a lot of bugs in Gingerbread.