I've not heard specifically that it's not.
The clock keeps rolling on your years of Commissioned Service, though. In other words, if you were commissioned in 1980, retired in 2000 as a Lt Col, and came back to ANG or AFRC in 2004 you'd still be forced to retire in 2008, as that would be considered 28 years of commissioned service.
It's a good deal, however. I've had two squadronmates who were return from AD retired. The best way to describe the pay issue is simply that they didn't collect retirement pay on the days they were paid by the Reserves.
Another good thing: Both guys in my squadron retired as Majors. They made Lt Col in the Reserves. Since we collect our military retirement at age 60, once these two guys hit 60 their retirement pay will be recalculated as Lt Cols with their points earned in the Reserves added, also. Very nice coin.