Not sure if this fits or not. Also, I haven't listened to the commentary, but isn't the Blood Simple commentary in character by the fake film historian?

There is at least one Space Ghost: Ghost to Coast commentary that has Zorak in character the whole time (not sure about other characters).

The Dodgeball Unrated commentary has pretty much a "fake" commentary, but they aren't in the characters of the movie.

I think everyone else mentioned some of the other ones off the top of my head: Spinal Tap, Family Guy, Mr. Show (Uggh... I love Mr. Show, but those in-character commentaries were terrible... luckily they stopped doing those after a while)

Muppets From Space has Gonzo and Rizzo in character. I thought it was entertaining.

i dont think thats a commentary.
thats an alternate language track featuring the movie played back in the language of the thermians.