If a person comes in and, without permission,
takes the image of their property and resells it
or reproduce their property, then it would also
fall under the category of property theft, not
just copyright infringement.  So, yes.  The cel
owner does own the rights to their own property.  

Example, you know how there were a lot of
artifacts recovered from the Titanic especially of
the dinnerware?  Well, there is a company that
went back and reproduced the designs of the plates
and dishes and sold them as repros.  They had to
first get approval from the ones who owned the
dishes and patterns in order to reproduce the
designs and give profits to the original
company/owner.

Now, cels are EXACTLY the same as this situation.
 The fan cel artist MUST get approval from the
copyright owners AND the ones who own the property
(the cel owners who paid for the cel) in order to
reproduce it.  This fancel artist did NOT get
approval of either person(s).  So therefore, what
they are doing is definitely illegal.

Star Phoenix