Update: First, a bit of clarification. AMD RAIDXpert2 is provided by Gigabyte in 2 formats. First a version of it is embedded in the BIOS. This version could see the HDDs but for some reason would not allow me to "Apply Changes" after setting up RAID 1. The second version can be downloaded from Gigabyte's support web page and is a Windows program. That version allowed me to see the HDDs and to set up RAID 1.
Next, I attempted to update my AMD chipset drivers. The updater from Gigabyte had a description saying it would update the drivers to 18.10, but when I ran it, it said I had 17.40 and would only downgrade to 17.12. Odd, and I didn't do that. Then I ran the AMD RAID driver upgrade. It didn't upgrade RAIDXpert2, but instead updated my chipset drivers to 18.10! Odd, but this time I said okay and rebooted.
After that I was able to see my HDDs as a RAID1 in Disk Management. I did a quick format and assigned it a drive letter and now it's working.