Ok I solved my issue.  Turns out there's a setting in iDRAC called "Hardware Configuration Validation" where you can just tell the system that yes, what you have installed is valid.  ???   "Accept current configuration as a valid configuration".  -> yes    So, I did that and the errors went away.
Hi,  We recently acquired an R650 that had formerly had 2 CPUs installed plus risers 2 & 3.  Turns out if you go down to a single CPU, you can't use risers 2 & 3 anymore, since they both leverage CPU2.  I'm reading that the only valid riser config for a 1 CPU system is "R2A + R3A (Config0-1)"  according to [URL] ... where do I actually find part numbers or a more robust description of what that means?
R650 riser configs