Does MarketplaceService:PromptPurchase() work with both gamepasses and Developer products?

I am creating systems for my game that are as modular as possible for easy addition of content and am wondering if I would need to specify if the product is a game pass or DevProduct upon purchasing of an item.

No.

For gamepasses, use PromptGamePassPurchase
and for Developer Products, use PromptProductPurchase

PromptPurchase is for normal assets such as Shirts, Pants, T-Shirts, Hats, etc…