Yep, for my file server, I have 3 Promise ATA cards (one of them is SATA) and then I also utilize the onboard IDE controller as well. In my particular setup, I have to use the primary/mainboard IDE controller as the boot device, or there is a conflict with the Promise cards.
Speaking of setting up large HDD storage servers, does anyone know of a good case to house 16-20 3.5" IDE drives? I always see the ones that house 5.25" drives/bays (I'm assuming for hot-swap and individual cooling solutions), but never for 3.5" drives.