The D3000 uses a CCD sensor that isn't as good as the CMOS sensor that are in the Rebels for shooting in low light. This is very important for weddings. Nikon released the D3100 that takes care of this flaw.
The second thing is to see what the brand the photographer uses. A wedding photographer should have redundancy in lens in case one goes bad, so you should be able to share with him. This will save you a ton of money to start, because the lenses you use for weddings will cost significantly more than the body itself.
I am new to the SLR world and I can't decide btw a Canon rebel or a Nikon D3000. I take pictures of just about everything, but right now my main focus is assisting a photographer during events. (ie Weddings and Mitzvahs) I have always had a canon power shot camera so I am more familiar with those, but I am not sure which camera to get in the SLR world. In addition, I would like to know what extra lens is worth getting. I personally would really like to get a wide lens for the camera but not sure which one to order. Any help or suggestions would be greatly appreciated!!