sudo and uids

[john test]

I have two users both with the same uid does sudo recongnize this and apply 
sudo to the right user?
ie
jane:*:6000:4000:jane doe:/home/jane:/bin/noshell
joe:*:6000:4000:joe blow:/home/joe:/bin/bash

if I give joe access and try sudo it says
password: 
Sorry, try again
x3

then stops.  Can somebody shed some light does sudo work with single uid 
environments.  ( I can't assign many uids because I am an ISP and have to 
many customers) .

redhat 6.1
pam disabled. 

thanks a hole bunch

johnnycal at ispchannel.com