Mazers will use potassium sorbate to stabilize mead, not campden tablets. It all depends on the level of residual sweetness you are going for. If you want the sweetness of the cherries add the sorbate so that the sugars can’t be fermented; if you want the mead to be dry don't add the sorbate and allow the remaining yeast to ferment the sugars.
Personally, I like dry mead, so I wouldn't sorbate. I don't like using any preservatives, so I stay away from campden tablets. Its all about preference.