Yes, a "pushbutton" is simply a "pushbutton" so it would not matter whether the pushbutton is on top of a joystick or simply on a control panel. For games like Zaxxon (which had a trigger button on it's joystick), you could easily play the game using a normal joystick with a pushbutton from your control panel instead. However, games which require the player to move a joystick, turn a spinner knob and push a button at the same time (ie: Discs of Tron) would be unplayable so you would have to get a joystick with a top button (or trigger button) unless you have three arms

Also, any game which required the used of two joysticks at the same time while needing the player to push a button (ie: fire bullets, etc..) would be unplayable as well.
Not sure how many games out there fit this criteria, but I think I answered your question