As has been widely publicized in the games media over the past 24 hours, recently 'Let's Play' and other user generated game-oriented YouTube shows have been hit by a number of copyright claims.
The issue is confusing and problematic. YouTube has attempted to use automation to enforce copyright policy, while the actual policies of game publishers toward YouTubers varies tremendously. Some publishers forbid any use of their content, others allow use of content as long as it is not monetized by the user. Others vary further, allowing/approving monetization to certain youtube networks or sometimes individuals, occasionally with certain usage restrictions.
For Hi-Rez Studios games, our policy is simple: We support and encourage you, as an individual content creator, to create videos using our game content AND monetize those videos as you wish.
If you are asked for written permission to monetize your videos, send an e-mail request to us at firstname.lastname@example.org. We typically provide personal responses & approvals within 24 hours.
More generally, we believe multiplayer games spread most effectively when gamers can see the actual gameplay for themselves. You are effectively helping to get the word out on our games and for that we thank you.