Assuming the H3 outputs the ambisonic audio in the proper format (I don't own one...yet), you can just load the 4 tracks of audio to Vegas audio tracks and trim it to length to match your video. With the H2, I believe you had to use software provided by Zoom to encode it. With my Vuze camera I converted the 4 microphone audio to ambisonic audio using the ambisonic toolkit for windows.
Vegas doesn't have any tools specifically for ambisonic audio.
Rendering 4 audio tracks is a little tricky, but is covered here: