Apple Watch ultra gps

Apple built a dual GPS antenna into Apple Watch Ultra. It should work, but I can't say I've tested it in a remote area without cell service. In theory however, that is what the watch was designed to accommodate.

That depends on whether you added cellular service to your Ultra? If you want to use the watch without cellular service, you must have your paired iPhone with you for it to function. If you have cellular service on the watch, and don't want carry your iPhone with you, you can do that and GPS , etc.., will work.

It's not clear from your question whether you are wondering if you can use the watch without it being paired to an iPhone? With or without cellular service all Apple Watches must be paired with an iPhone.