So the quick answer is yes it has happened before, but with a caveat. In the earliest years of the MOP award (starting in 1953) the eastern and western teams did not play an interlocking schedule, so the only chance for them to meet was in the Grey Cup. So in 1953 the MOP was Edmonton’s Billy Vessels, but the Tiger-Cats beat Winnipeg in the Grey Cup, so he did not face Hamilton. It happened 3 more times in the 1950’s when the Esks Jackie Parker (in ‘57 and ‘58) and Johnny Bright (in ‘59) won MOP but Hamilton and Winnipeg played in the Cup each year. By the time Montreal’s George Dixon won MOP without playing in the Grey Cup, CFL teams were playing a full interlocking schedule, so he faced the Bombers in the regular season.
I haven’t done a deep dive through the rest of the 1960’s and 1970’s, but as far as I can tell, the MOP for each season from 1980 to 2022 either played for or against the eventual Grey Cup champions for that season.
There were two close calls though. In 2002 Milt Stegall did play against Edmonton in one game, and started the second before being injured early, and then did not play in the playoff game as the Esks went on to win the Cup. In 2004 BC’s Casey Printers won MOP and did play eventual champion Toronto at home in August as he was replacing an injured Dave Dickenson. He’d play a bit of the re-match in Toronto before being pulled midway through a loss. And then he famously was sat for the Cup in favour of Dickenson three days after winning the MOP, and the Argos won.
Now since the whole implication of this question is that Kelly sat out against the Bombers in their lone meeting and the Bombers are destined to win, if you have now angered the football Gods with your presumptive confidence and jinxed us come this Sunday if the Als pull off an upset, and made me do all this work to boot, then