Are the Munchkin original and Munchkin Guest Artist Editions identical?
Munchkin Guest Artist Edition is identical to Munchkin Deluxe, just with the cards and board illustrated by different artists. 

From the Munchkin: GAE web page:


  This Guest Artist Edition includes completely re-illustrated game cards, a new gameboard decorated with Ian McGinty's interpretation of the Munchkin world, and male and female standies for each player.


Other Munchkin properties that have Guest Artist Editions follow suit in a similar fashion.

UPDATE: I double checked with SJ Games just to flesh this answer out a bit. Their response to my twitter message was this:


  They contain the same cards as their respective versions, just all new art, yes. -HS