Ugh. I didn't like that discipline in Wod. The last time I saw it was the last time I wanted to see it. The dang thing blackens the whole screen + GUI. If you're unfamiliar with what happened, you'll think the game just broke. Bad idea. There's got to be a better way to do that.
Last time I looked Shroud of the Night simply created a black domeshaped object the surrounded the player, your character can see inside it and around, if the enemy cant see anything its because thats how the discipline affect others, it didnt affect my character in that way, dont think it makes the GUI disappear though.. I used WoDmod 1.2 so I never really encountered what you say in that mod but could be thats because my own character activated the discipline.
I guess the real question is if you can make the darkness gradually blacken the enemie's surroundings without affecting the GUI or Chatbox? Yeah I guess you can if you creat a very black object that constantly blocks the enemie's camara while he is inside the AoE zone.(but doesnt block the caster's camara)
The other way I was thinking of is effect on the enemy so everything (Characters, NPC, Objects?) become invisiable to him while inside the dome and his screen turns to a Dark Blue/ Grey Tint and text appearing in bright telling him of the effect taking place (which still allows the enemy to see the client is not dead and its a discipline effect) The Character would be able immobolized with all the effects on its stats and will be able to move only after commiting a relevant roll per turn( Per+Athletics? Diff +2) to emulate the confusion aspect and difficulty of moving blinded and a Simple Diff+2 to all other actions as described by the corebook.
Also its important to know that effect to some extent could be negated by use of Lure of Flames or holding Tourch (in short the shroud doesnt extinguish fire based lightsources)