I'd be surprised if it worked. To get to that high a resolution (2560x1600 for the 30" Apple Cinema Display) you need dual-link DVI. The specs say the monitor will fall back to 1280x800 with a single-link DVI connection. Unfortunately, single-link DVI is all you'll get out of the V12, with or without the DCD option (according to old posts in these forums). The DCD gives you two separate single-link DVI connectors which is very different from the required one dual-link DVI channel (which is actually a single connection with more pins for higher bandwidth).
See the Wikipedia article on DVI
for more information about the differences between single-link and dual-link DVI. A forum search will turn up many posts about the lack of dual-link DVI on SGIs.