After receiving support from Unity, we discovered that the info.plist row should actually be "MetalHudEnabled=YES". The official presentation video says to use "HUD" in all caps but that is not true. With this I am able to toggle the Metal Performance Hud on/off on command from my program. Hopefully this post helps anyone else attempting the same functionality.

I've attached an expanded screenshot of the info.plist to demonstrate XCode's indenting.