You could say "Gate pass has not been issued" if it is a short notification needed by a machine at a gate, but not "Gate pass is not issued". However, if it was to be a sentence you would say. A gate pass has not been issued. This sounds better and more polite. If a gate pass won't be issued you would say for example. A gate pass won't be issued, because you have to work here to get one. OR A gate pass will not be issued.

It's a question of time. If this is a notification message, then "Gate pass has not been issued" is correct. If this is a general statement, then use "Gate pass is not issued".