Ah okay.....
/me waits for other people to contradict .
Rogue has been contradicting Downix for a long time on this matter. Recent statements by Rogue have declared DMA to be known working with some functions of the AmigaOne board under OS4 (like ethernet, as Downix noted is able to utilize DMA). IDE DMA has been said by Rogue to be working, but not with the driver system of OS4 yet, not because it can't, but because they haven't yet implemented it in the driver.
This was just a day or two back at AmigaWorld.net
Paul