Welcome to the forum birdy :thumb: .
I presume you are talking about kits? Well all that you mentioned like granulated sugar are 100% fermentable (or as near as dam it). The problem with this, though kit instructions ask for it is that they add no body or mouth feel to the beer, what you end up with is a rather thin beer. You would be better using Dry malt extract or liquid malt extract as this is malt and will add body to the beer.
You could however as you say use treacle or golden syrup but only in small amounts as they will impart some flavour, treacle being quite a good idea for a stout or dark ale, but only a small amount.
:thumb: