I found this online:
When a Molasses container identifies the product as "sulphured" or "unsulfured" the terms are used merely to advise which Molasses were refined using sulphur dioxide. Sulfured Molasses are made from young sugar cane, which requires sulfur dioxide during the sugar refining process. As the sulfur becomes mixed into the Molasses solution, a change in flavor occurs, reducing some of rich taste generally provided by Molasses not processed with sulfur dioxide. Unsulfured Molasses are made with more mature raw materials and the juice is clarified as it is processed, producing a higher quality, thicker, sweeter, and better tasting grade of Molasses. Unsulfered Molasses are typically preferred for recipes in order to provide a more pure flavor.
I don't think it should make any difference which you use -- the flavour of the pumpkin and ginger in your recipe would probably cancel out any slight variation in taste between sulfured or un-.