I have never had gammon but i would think it should pair wonderfully with pineapple. We pair pineapple and ham all the time and it is delicious. We also have a form of tomato gravy with ham but I wouldn't call it tomato soup.
Ours is a tin of Heinz Tomato Soup, heated and popped into a gravy boat. Pineapple and gammon work just fine together, just with a stronger taste than ham once cooked. It's just that nowadays I enjoy my ham / gammon to be full on savoury rather than with the sweetness of pineapple.