Well it doesn't hurt to ask.  Some fancel artists 
are very good with originals, some suck.  
*shrugs* Last original cel I did was a gundam x 
cel for Keeper (first cel in my 5th gallery), and 
she was as vague as 'this character in a pose you 
think is characteristic'.   I didn't even know 
the character, but I did research.  It was fun.  

For me, original cels are usually the most 
enjoyable because of all the possibilities, cels 
based off of existing images can be challenging, 
which is good too, because it helps your skills, 
but straight reproductions are about as 
interesting as a paint-by-number.  A paint-by-
number you didn't even pick.  >.<