This class is a great reason to keep your Charisma high.

It takes one of the least useful abilities of the warlock and makes it as awesome as it should be.

Hungering dark by itself is very interesting since it basically creates a constant pseudo blast shape. Sure you can only target a number of enemies up to your blast dice, but damage isn't really the point here. This is a controlers dream I think.

Question 1: The DC mentions class levels, I presume thats the levels in Emissary? (Not sure since you use the eldritch blast for it which comes from the base class)

Ravenous Gloom:
I have to agree that the poison seems a bit weak. Though its still useful.
The extra damage one is nice, but damage output isn't really what the emissary excels at.

Negative level? Awesome. (Do they stack?)
suppressing DR and SR is also very very good. ESpecially the latter if you wanna help your own wizard or run around meleeing in there.

Resilient Shadows: In my opinion this is the best part of the class. Your darkness suddenly is a lot less likely to be dispelled and your Ravenous Glloom abilities have a better chance of hitting SRed enemies.

Cloak of night: Is this calculated starting at 3rd or does it take the full levels, because 70% miss chance at level 5 makes you nearly untouchable in there.

Gloomsight: You see everything while everyone else is grasping in the dark.

Impenetrable depths: Something I noticed and am very hyped about. Does this mean that for anyone not able to see in magical darkness you are unhittable if farther away than 10 feet? Since Cloak of night should basically add 50% to the already existing 50% you are 100% concealed. You are now literally untouchable for ranged enemies.

Midnight shroud: At this point, once you activated your darkness no one is really able to do anything to you unless they [Light] nuke the entire area.

And now for cheese:

Drow of the Underdark has this handy little feat that only specifies that you must have Darkness as an SLA ... and transfroms it into deeper darkness. Your playground just got bigger ... and longer lasting ... and one level higher (so at character level 10 you have a 60feet radius playground that can't be dispelled unless your enemy has a level 9 light spell handy. YOU ARE THE DARKNESS)