I guess you know you've really made it when Rockwell draws you
Yep. You sure have.
(Rockwell called this painting "The Blues Singers"; the original now belongs to Al Kooper himself---Mike Bloomfield died in 1983---after it hung for years in a Columbia Records office. If the Miller portrait wasn't used on an album jacket, that would make The Live Adventures of Mike Bloomfield and Al Kooper the only album jacket Rockwell was known to have painted under contract.)
I think that is definitely the case. I can't find any album of Mitch's, at least for sale online (Amazon,Barnes and Noble), that features the Rockwell rendering on the cover.