I've tried to add this link as a service and it hasn't been working. I'm starting to wonder if it is even possible.
That's the link to the metadata page, not the service URL. To add this layer as a Web Map Service, you need to use the WMS service URL.
Get the WMS service URL by right clicking on the "WMS" in the upper left of the metadata page, and choose "copy link address". (If you're using a Mac, do whatever the Mac equivalent of a right click is. Probably command-click while eating a slice of apple and listening to iTunes.)
The WMS service URL is:
In your Browser panel, right click on WMS/WMTS > new connection > paste the WMS link and add a title for the layer. Click OK, then double click on the new layer in the Browser panel to add it to your map.