Hmmm. Given the tight quarters the 18-105 might be the best choice, but that's not one of yours.
Looks like some bands bring lights, others don't. Find out what they have and how close you'll be. Clubs like that, for a metal gig there will be (hopefully) be sweaty fans pressed up front, so most of your shots may be from the side, and any up from will subject you to getting knocked around which will be bad for movement. I don't like the idea of flash in places like this, but if you have to use it it'll likely produce better black and whites than color images. Not a bad thing, but something to consider when you talk to him. The D3100 isn't the best high ISO camera, so in your practice see how high you can crank it to shoot without flash and not get more noise than you want. ISO noise can always be disguised as film grain in B&W's too, so consider that.
Doing a practice run at the place sounds like a must. Bring both lenses with you both times just in case. You don't want to wind up with the wrong one. Shoot a bunch with one, swap out on a break and shoot closeups with the other.