I believe you want to use Get Axis with the Axis name Mouse ScrollWheel, that will give you a float.
That worked, thanks.
For those of you who would like to do the same thing:
I have a "Setup" state with a "Get Property" which gets the field of view from the camera and stores it in a "Field of View" variable. After that's stored the state enables the "Finish" event which transitions into an Zoom state.
On the Zoom state I have a "Get Axis" which stores the 'Mouse ScrollWheel' Axis Name into a 'Scroll Wheel' variable. Change the multiplier to something lower/higher than 1. I used -50 and that worked well for me. (I used a negative number to reverse the zoom direction.)
Then I have a "Float Add" which takes my "Field of View" and adds "Scroll Wheel" variable.
And finally I have a "Set Property" from my main camera which replaces the camera field of view with my "Field of View" variable. All of these have Every Frame checked.
Now you can zoom in/out with the scroll wheel... I hope that helps someone!