We have "no DRM", but we do retain full control and manage the copyright on all of our material.... and all of our material is copyright.
DRM is an add-on and has nothing to do with copyright. DRM is all about restricting access and controlling distribution and when overdone, can be annoying. Copyright is about protecting the rights of the creator and grants the creators of original material, the exclusive right to exploit their work. We can contract out some of those rights to publishers, etc., but the copyright remains ours.
Your YouTube videos of gameplay can be considered game reviews. The copyright material used in the review can't be sold, just as a game mod can't be sold. The website that the game review or mod, etc., is posted on, can have paid advertising on it, which can earn you revenue. It's a grey area and if significantly large, usually requires legal clarification.
To avoid confusion it is always a good idea to post a copyright notice such as "all game material and related logos are copyright Longbow Digital Arts".
So, based on what you are doing now, there shouldn't be a problem, but you can contact me directly about any specifics.