I think historically pumpkin was used as a fermentable but it’s widely accepted that the spices used make the flavour rather than the pumpkin. The term ‘pumpkin spiced‘ seems to dominate everything form candles to coffee come autumn time especially in the USA and feels more apt a term. Due to the nightmare of adding pumpkin to a mash it’s generally considered more hassle than its worth what with the flavour being from the spices - cinnamon, nutmeg, ginger, clove etc.