... and they'd want the RAID functionality, once established, to be transparent to the user, and therefore to work with normal function calls.
The only low-level systems I know of that prevent Eraser working are those (such as wear levelling systems on SSDs and flash drives) which redirect the erasing write to a different physical location on the drive. In such cases, the erasing data is written but the original data is not overwritten (though a free space erase will work, because that fills the drive). I do not know of any reason why a RAID driver as such should include wear levelling; that is a function of the individual physical drive rather than of the array. Of course, it is possible to use SSDs quite effectively in RAID arrays; in commercial applications, such drives use encryption to protect the data.
David