Update. Flew Air Europa LGW-MAD. Initially had issues putting in my Skymiles # and it said there was an issue, but it all worked out. Was able to check in, use extra bags, and Sky Priority was printed on boarding pass. Unfortunately, they still wanted me to pay for seat selection above row 18 (discounted), as opposed to free with KL/AF at OLCI.
Flight experience was ok at best (ontime), but the onboard product seemed stingy. You had to pay for everything onboard beyond tapwater (juice was extra). Plane itself was a little tired looking with no onboard power, and the armrest in front of me broken. Waiting to see if my mileage posts....