Do I need to run a resolver in order to use GS1 DL?

No. Brands can use the GS1 DL syntax on their products today, using their own domain name, and provide a simple one barcode to one page redirect, without using a resolver. Any webmaster will know how to redirect from one URL to another. Later, they can add in a resolver and thus provide multiple links from that one original DL URI. This provides an easy glide path from the current to the future state.