Well, this turned out to be easier than I thought. As I said, I was told by multiple techs that RAID drives are proprietary and non-standard, and so are useless without the chassis it was written in.
To test if the Linux reader solution was going to work (before I needed it), I bought a very cheap (<$20) SATA drive to USB docking station so I wouldn’t have to disassemble my PC.
I have 2 of the mirror devices from Western Digital, a My Book Mirror and a My Book Studio Edition. I removed drive B from the My Book Mirror. I started the Disk Internals Linux reader program and plopped the drive in in the docking station.
Much to my surprise Windows mounted it without needing the Linux reader. It showed up as a very standard NTFS volume with the whole drive accessible without needing the reader and using the standard Windows Explorer.
Thinking there might be a difference in the 2 boxes, I then tried the B drive from the Studio Edition. Same thing. It reads just find without needing any help from Disk Internals.
So, the RAID advice I got may not be entirely true, at least not for these Western Digital RAID 1 mirror drives. They appear to be entirely standard NTFS volumes.
It may be that the chassis is using a reserved area of each drive to work this magic, but whatever they’re doing doesn’t seem to affect Windows at all.
So this is very good news and makes recovery of my data MUCH easier even if the chassis goes up in smoke.
Quick note to the Googlers, the drives are a very tight friction fit in the chassis and require substantial effort to slide them out.