How do you edit in multicamera mode if you have a mask on one track?
Here's what I ended up doing.  I created a mask the way you would normally create a mask, and the end result was that I had 2 video tracks.  Any tutorial on the Internet can show you how to do that.

When I got ready to create my multitrack edit, I included every video track except the 2nd video track mentioned above.

In other words, let's say I have 3 video tracks; V1, V2 and V3.  V2 is the camera angle where the person's face can be clearly seen, so I put a pixelated mask on the person's face for the whole clip.

When I make my multicamera track I only highlight V1, V2 and V3,  This combines those 3 into one track, and V4 remains it's own separate track.

Now when you make the cuts and edits, that pixelation mask will still be on any shot where you use V2 as the source, but will not be on any shot where V1 or V3 is the source.

Just remember, when you render the video make sure the mask track, the one you didn't add to the multicamera track, is above the multicamera track in your track layout so it lays on top of that track instead of under it.