So I decided to ask General Tire directly about the change in recommended wheel widths for the 275/55R20 size for the Grabber UHP. They basically responded saying that the 7" recommendation was a typo.
They also included in the response that proper inflation will likely cause premature center wear and that under-inflation to balance the wear is a safety risk. Needless to say, I have contacted them back on this as those don't seem to be acceptable outcomes for a tire I was led to believe would actually fit.
The kicker is that the final 2 tires at this size that appear to be listed for a 7" wheel width (Grabber HTS and Continental CrossContact LX) are both under the Continental brand. This likely means that those being listed as compatible with 7" wheels is also inaccurate, which would leave 0 options in the 275/55 range for the OEM wheel...
So, after a bit of back and forth, General Tire decided to do a good will reimbursement at full price I paid for the UHP tires since they are not recommended for the 7" wheels I have. They initially said I could pick out any General Tire set of tires for the vehicle and they'd do that exchange no problem. However, they told me they don't make a tire for the 7" wheels. They told me they based their ratings on ETRTO standards, which ultimately means that the 275/55 tire is not suitable for the 7" wheel width.
I'm still assuming in all of this that they are also acknowledging the typo applies to the HTS and the Continental tire as well (which would mean that there are no 275/55R20 tires suitable for the Limited 7" wheels).
I took this opportunity (full refund) to go with a set of Firestone Destination AT 275/70R17.... on a set of Countersteer Type X wheels....