Yes, you can talk to your team members in-game with the PS2 headset.
When you've got good people on your team, it's awesome. You can coordinate actions and operate as a real team. However, far too often I run across:
1. Guys who think it's funny to sing, ramble, or say "poop" over and over
2. Kids who think we need a second-by-second update about their actions, scores, or soda intake
3. People who don't realize they're broadcasting an argument with their little brother/mother/girlfriend to 7 other people
4. Idiots who verbally abuse teammates
Now, I put the headphones on when I start a game. If someone starts bugging me, I turn them off. This usually leaves the headset off half the time.
I still think it's a great feature, though.