Let's Plays & streams, and with them the monetisation of your videos, are permitted for all games as long as you insert the following in your video descriptions:
Please always refer to the Steam store links of the game
Please copy this into the description:
"Join the Kalypso Community!
http://www.facebook.com/kalypsomediaInt
https://www.youtube.com/user/kalypsomedia
http://www.twitter.com/kalypsomedia
http://www.twitter.com/kalypsomediaUSA
http://www.twitter.com/kalypsomediaUK
Have fun playing!"