There are the Linux drivers for your chipset. I don't think any of the precompiled ones will work though. They do have the source.
I don't understand the grub error. I suppose that you need to have the chipset drivers installed in Linux so that grub will properly recognize the array as a drive. I do know that you need the drivers installed if you intend to access the array. You will also need support for NTFS.
First I would suggest physically disconnecting the raided drives, installing FC on the other drive and confirm that it will run. Then get the High Point drivers going. Then reattach the array drives and after determining what their drive designation is I would modify grub to point to the array for the Win boot.
I had a mb that had a hotkey during the boot process that brought up a menu allowing you to select the drive to boot from. Actually, I beleive it was two different motherboards, one Intel and one ECS. If the mb will do that I suppose grub doesn't need to know about the Win array.