There is in the settings for DayZ an assignment option for Ctrl + middle mouse button (ctrl + mouse wheel depressed) combo, however there is none without that ctrl key in the menu, which seem strange to me.
The way the options for assignments are set up for DayZ makes any use of a mouse wheel depress (the mouse wheel can be used as a button and not only for scrolling) somewhat tedious when also having to press the ctrl key.
Example of desirable use:
When pressing right mouse button, you can zoom in with the camera, however there is a delay this way. Pressing the plus key allow you to zoom in with the camera instantly, but you will have to move one of your hands to the numerical keyboard. Now, it would be nice to be able to use the middle mouse button (mouse wheel depressed) to use as an instant zoom.