From what I've gathered while reading from early adopters across the internet, never "assume" that it'll work.
Unfortunately, I can't test the card's bootability, because I don't have a spare hard drive to throw an OS on, to test with. Right now, the system with the Sil3114 controller, contains both a Promise Ultra133 TX2 (this is the boot controller) and another Siig controller based on the Sil0680 chip. The system's got a hodgepodge of drives ranging in size from 120 GB to the 1 TB, that I mentioned earlier. The current BIOS that's running on the Sil3114 controller is 18.104.22.168. I know that there has been (at least) a newer release since this one.
The PCI Sil3114 controller is a Siig "Serial ATA 4-Channel PCI", part #:SC-SA4011-S2. It's supposed to be bootable, and coexist with your on-board and add-in controllers.
The other system's motherboard, that's in question, is a Foxconn NFPIK8AA-8EKRS, running BIOS dated 3/7/2005 (there is only one newer release since this, and it only added support for dual core Opterons, so I never bothered to upgrade it - in fact, Foxconn recommends not upgrading the BIOS unless absolutely necessary).