The GUI for artifacts is still displayed on screen with Dungeons Gear removed.

As a side note, I have Dungeons Mobs and the library mod to go with it. If the library mod is rendering a GUI dedicated to the gear mod, perhaps it should have a dependency check?

Dungeons Mobs also contains several artifacts that can be used, these are a bit rarer, but hence why the bar is still there.

You can disable the bar using a texture pack.