Is it possible to utilize different types of controllers simultaneously on the 2600? ie, using a joystick and either a paddle, the driving controller, or the trackball? Has this ever been done on a published stella game?
Definitely possible, as long as they're plugged into different ports! So you could have a pair of paddles in the left controller port and a joystick in the right controller port, or a joystick in the left port and a keypad in the right port, and so on. The only game that comes to mind is "Star Raiders."
G.I. Joe - Cobra Strike (called Action Force outside the US) uses paddles and joysticks, supporting up to 3 concurrent players. The paddles control the shields & gun turrets while the joystick controls the cobra.