Has a dual-boot over RAID of OSX and Windows been done to begin with?
With hardware, Yes, IIRC. But I've not yet seen it done successfully with OS (software).
I'm guessing, but a fake RAID solution should work as well, as the drivers are supplied by the manufacturer, and the technique (low level operation) should be the same between OS drivers. Finding one of these that can boot on both a Mac and PC may be difficult to find though.
I've not looked for one, so I don't know for sure.
AFAIK, certain RAID cards need flashing for booting either Windows or OSX.... Or with Areca's cards, is the flashing just for EFI support, regardless of OS
Highpoint can only hold the EFI or BIOS version of firmware. If you're using Linux and Windows, the BIOS version can boot both, but if the EFI variant is loaded, only OS X will boot.
As boards switch to some form of EFI (UEFI 2.1), this would hopefully change, but it won't help currently. (I've only seen an MSI board running UEFI 2.1, and it was an experimental).
Areca apparently can do multiple OS's.
The EFI is an add-on as I understand it, but there's a member here who got it to boot into OS X without even installing it.
Atto as well, but I've not ever used one on a Mac, and can't say from my own experience this is actually the case.
I'd sent emails to both companies about this, and didn't get a clear answer from either.
I don't have a Mac anymore, nor have I yet made my current machine a hackintosh. So anything I might manage to do (Areca's), would only have implications in the hackintosh community.