It varies with different games on Steam. Steam doesn't require its DRM, so some games have no DRM, even when installed by Steam, which is great. More critically, though, Steam also doesn't require its DRM be exclusive so some games are protected both by Steam's DRM and something else, where that something else may have its own weird requirements before launching a game.
Can confirm. I bought Goat Simulator from Steam about a year ago, have uninstalled Steam, and even moved the application between OSs and devices without any issue.
That's why we should promote DRM-free software distributions - like GOG.