Your question actually poses a lot of challenges. Cooking with cheese can be a challenge in the best circumstances, because of its tendency to separate and produce a stringy, tough mass when overheated. Hard, ripe cheeses work better than soft cheeses, and in a sauce, or tempered with wine or some other acid it is more stable, but the primary fact remains: cheese can stand up to only so much cooking.
For that reason, we would advise against cooking it in a slow cooker, and – sorry to say it – also against keeping it hot that way. Anything with a large amount of cheese should be cooked gently, according to the recipe, and is best eaten immediately.