Why not? As with anything you’re doing for the first time, though, we’d keep a pretty close eye on it. Slow cookers are not of uniform quality, and what might work in one might scorch near the heating element in another. An apple butter recipe in an older edition of Joy of Cooking (Canada, UK) lets you finish it either in a watched pot on the stove or in a casserole dish in the oven. If you choose the oven, the recipe suggests you reserve a quarter of the fruit purée, and add it to the rest once it has cooked down substantially. Then cook it a bit longer until the right consistency is reached - thick but still moist.
With this method, you can ignore it entirely for a while, but still achieve the right consistency. Of course, the heat of the oven is uniform, while the slow cooker may not be. Some have the heating element at the bottom and others have it running up one side. It is for this reason that you will not want to ignore your first batch of cherry butter. And because you’re heating it in order to get the water to evaporate, don’t cover the pot.