If I was saying this in English I would leave out the second article and just say "is it a skirt or dress?" Is this done in dutch also, or are articles always used?
Not necessarily so. In English, one can use the article in front of both items, usually for emphasis. It's a matter of taste though.
What I cannot say is how the articles work in Dutch. To this end, I'd say let's stick with this format until we get a substantive statement from someone with a deeper understanding of the ins and outs of Dutch.