I had a similar problem and did not know the proper procedure either or wanted to work with dell to find out. In my case I had a SATA cable go bad. After I got the new cable I made sure the drive with the good data was plugged in to SATA port 0. Booted up and broke the RAID Array. I think I did this from the RAID screen that you see just after booting up and pressed CTL I.
I broke the raid array. Connected the new cable to port 1 and drive that was not in sync. After boot up I went to the Intel Accelerator and selected the option to migrate to RAID 1 array and choose to ADD SATA Drive port 1 to the array. After about 30 minutes for a 120 GB drive I was back on RAID 1. I think I had to boot after the migrtation and maybe one more time after it came up on RAID 1.
Everything has been working fine since replacing the cable.
Thanks for the update. The warning does look kind of bad the way I did it, but I was not too concerned because I figured on a RAID 1 break I would end up with two drives with the same image. It worked for me. But the procedure you documented seems to be better. Have to keep that in mind if I ever have to do that.
I think Dell could do a better job of documenting the procedure. I am not that confident If I called Dell Support and waited the 30 minutes on hold I would get the right answer.