Originally Posted by Steve M

That's true. But unless they've taken them out, LAS also has airport-provided universal check-in kiosks that will allow you to check in and print a boarding pass for any airline. You won't be able to check bags, but unless those airport kiosks are gone or they've deliberately programmed them to not allow UA check-ins at Terminal 1, you should be able to check in and print a UA boarding pass in Terminal 1.