VO with GPS setup

I am pretty new to multicopter design, and I am trying to choose the sensor stack. I have a pixhawk with ardupilot and m8n GPS module. However, I want to use Visual Odometry as well. I have found the vision position estimate message, which I can use to feed VO data back to ardupilot, but, all the implementations I found use it as a substitute for GPS data.

I am wondering if it is standard/possible for EKF2 to fuse VO and GPS data?