The discounts used in eCart are for the entire cart not for individual items. The discounts are accumulated and held in the cart, you can check on the total for discounts with some code like this:
if (WA_eCart_GetDiscounts(eCart1) > 0) then
This GetDiscounts function will get the total for the discounts, you can check it just like this if statement. If the total is greater than 0 then there is a discount for the current order.