How does 4-quadrant metering of 3-phase electricity work?
As you already know, 4-quadrant electricity meter just means it can measure the flow of power to the customer even if it is a reverse flow.

Your concern is whether generation and demand is recorded separately, or if the meter only records the net power flow. The key is that your meter is a "multi-phase" meter. Because your generator is connected to a different phase than your load, your ACE6000 can record the flows for each phase separately and independently.

You can see that each phase is measured and recorded on page 7 of this manual for the ACE SL7000, a brother to the ACE6000.

http://jocuccok.files.wordpress.com/2011/03/itron-ace-sl7000-tb-gb-0903.pdf