Allen,
Greetings. No limitations I am aware of.
Let's stick with one system for troubleshooting. Please provide your full system specs. Also, is this an existing windows installation? Meaning was it built and installed to an m.2 in AHCI mode and now you want to convert to RAID and add member disks to a different array?
If existing, how was the boot drive formatted? MBR, GPT? Did you install as Legacy or fully UEFI compliant?
A seamless boot is not always possible after switching the controllers operate mode from AHCI to RAID, even though the drivers are similar. Member disks can be included/excluded from a RAID set and be the primary boot device as a standalone disk. The only limitation being you must use "like" disks (same type of interface) for RAID.
I suspect this is related to drivers and/or Legacy mode, but need more information/history for a clearer picture.