From what I have read on here, it can't hurt... they may be more likely to put you on their slate because they have a bit more assurance that you will not be a wasted spot. Good luck!
I pretty much agree MMMom, except that there is no such thing as a wasted slot... someone on the slate will be accepted.
Not true. If no one is found 3Q on the slate, then someone from that district will not be charged to that MOC. It does happen.
As far as helping/hurting, it really depends on how the MOC views that. If your district is EXTREMELY competitive and you received a nomination from another source, they MIGHT NOT nominate you in the hopes others have a shot at receiving an appointment.