One of the reasons I don't bother using eSATA cards and drives is that they are very spotty with booting MacOS. Apple does not specifically support this, just Firewire and now USB also for Intel Mac's.
Some cards have advertised that they can boot a Mac, but OS's change and they do not...
According to this page, that card was designed to be able to boot MacOS on a G5 or PPC Mac:
http://www.amug.org/amug-web/html/amug/reviews/articles/firmtek/2se2e/
I don't know if they support this on an Intel Mac with Snow Leopard. In addition, Firmtek has new drivers for the card and Snow Leopard:
http://www.firmtek.com/download/
but if you need drivers to see a card, or the drives, then it probably won't be able to boot a Mac.
Here's the write-up on their new driver:
http://www.storagenewsletter.com/news/connection/firmtek-apple-snow-leopard-comp atible-driver - The word "boot" is not on the page, so I'm not sure.
Interesting page about eSata and Snow Leopard:
http://forums.creativecow.net/thread/8/1051087