Steam is not DRM.
DRM either
- Limits the number of installations
- Requires for you to be online to play the game
- Prevents you from using 3rd party software that modify the executable when it's running (like trainers)
EU4 will require none of these.
Steam isn't DRM all of the time. Though a number of games require a first time authentication from the Steam server before you can play the game in offline mode.
Honestly, I could personally care less whether it is DRM or not, what is more worrisome to me is how it is getting its tentacles into every single game these days. Soon, you'll have no choice but to install Steam if you want to play a game, and since Steam also sells the games you may as well buy the game from them too, and that will be a sad day.