Some interesting comments here, but the best advice is to ask to see an example of footage shot in dim lighting and decide for yourself whether it looks good. Some cameras are better than others in poor lighting but lux ratings don't tell the whole story, and knowing how to manipulate dim footage during editing is also part of the equation.
Although I respect my colleague's opinions, I must disagree..
Since we're responding to a bride here, and since "dim lighting" is such a relative term, I don't think we can expect her to ask for samples of dim video and make a decision. Besides, what videographer would actualy show her grainy, video lacking proper saturation?
Some cameras definitely are better low-light tools than others and, in my opinion (and probably the opinion of most), the previous poster has already mentioned the two current leading "wedding video cameras" for standard video. (I'd add the Sony FX1 as the leading hi-def camera due to its low-light abilities).
As for, "manipulate dim footage during editing" - this has got to be a last resort option and should never be part of the original equation. There is no time you're going to end up with better images having to correct things in post than if you'd exposed properly to begin with, so this should be a "Plan-B" option, only.
Shooting manually means nothing if you're not good at it, and in many situations a camera's auto exposure will do the right thing faster and better than a human operator could - the trick is knowing when to go off auto because that's not delivering the desired result.
We're talking about professional wedding videography here, so "..if you're not good at it.." should not even be a consideration. There is currently no prosumer video camera with auto-exposure that knows when to ignore bright or dark backgrounds, etc. Not a single model is intelligent enough to know what is the subject and what should be ignored. This means that in all cases where non-subject matter makes up a sizable portion of the image and where such matter is a contrasting luminence (darker or lighter than the subject) - the exposure will be wrong - GUARANTEED.
Also, only the camera operator can know if he wants to expose for the white gown, or for the flesh tones. It depends on the shot and what he is wanting to emphasize. No auto-exposure mechanism currently available can know these things.
Simply put, for the best results, the greater the camera operator's skill and experience, the less automatic control he will allow the camera to take. That allows perhaps a little wiggle-room for occasional use of auto-controls, but not much.
I am back in agreement about the multiple cameras. Ceremonies are all different, but most are best covered with either three or four cameras. Two should be considered a bare minimum.
Multiple cameras are great at receptions too, but here mobility is even more important and like the poster says, you don't want either cameras, tripods or camera operators to be obtrusive. I've been guilty of leaving a static cam or empty tripod where they show up in video shots and photos, and I have to make an effort to remind myself to not do these things.
