MSFS captures some controller inputs in "background mode" and uses them in-game, even though another window may have the focus. 

Example: (1) Load up any flight, (2) switch to an external view so you can see your aircraft's elevators, (3) click on your internet browser to make it the active window, and (4) move your flight controller up and down. You'll see the elevators in your aircraft animating and moving up and down, even though MSFS is no longer the window that has the focus.

My issue: it seems only the primary flight controls are available in this background mode, but I would rather have access to a different hardware controller moving different things--not the controller that moves the flight controls, but a separate joystick that controls the views. In other words, I'd like to use a joystick (not the one that operates the flight controls) to move the camera around while MSFS is not the window with the focus.

For moving the camera, I have a separate joystick that does literally nothing on my system except run the cameras in MSFS, so there won't be any issues with clashing priorities. It's just a matter of getting MSFS to accept the camera's pitch and yaw axis from a controller while operating in background mode. 

Does anyone know if this is possible? Any suggestions?

Drone Camera.  I use an XBox controller.  Works fantastic.

8 hours ago, prolixindec said:

For moving the camera, I have a separate joystick that does literally nothing on my system except run the cameras in MSFS, so there won't be any issues with clashing priorities. It's just a matter of getting MSFS to accept the camera's pitch and yaw axis from a controller while operating in background mode. 

All game controllers should work for this since their input are all "captured" by MSFS (as long as it is the only game running).
For camera control, an Xbox controller is used by many. You could also use another device as long as it is configurable to send commands via Directx / DirectInput