Is it possible to access NMIS in view-only mode without logging in?
Alternatively, is it possible to send login credentials through the URL itself?
There is no way to turn off the login page. However, you can setup a generic user account and give it the set of access you want. Then, the message displayed on the login page can be changed in /usr/local/nmis8/conf/Config.nmis to show the new credential set you assigned for View rights.
As for using a URL token, we do support a tokenized login via the URL in NMIS' commercial modules, like opCharts. This requires you to authenticate the user through some 3rd party method, then pass a token to the module the user is logging into. Of course, NMIS is open source, so you could expand it (as many of our users do) to accomplish exactly what you're looking for.