Just tested the Devilsight and the Darkness spell combo on my warlock and got disappointed that it didn't work as intended.
Right now it seems that Darkness is just a reskin of the Fog spell and Darkness Arrow. Loved the combo when playing regular tabletop DnD and would love to see Larian add this unique interaction into the game.
Yeah it looks like spells and items, including devil's sight, that provides darkvision haven't been implemented yet. At the moment you can only get it from your racepick.