If the ethicist's utility function is broad enough in scope to subsume (or at least recognize) that what is good for the economist is ultimately good for the rest of the system (if that were the case), then there might not necessarily be a need for distinction of utility functions.
It is possible the economist's utility function might hold some underlying (and unintentional) positive ethical effect.
The subsumption operates in the other direction. Utilitarian ethicisists can alway be modelled as rational agents with a specific set of preferences. Purely selfish agents can only be described using the language utilitarian ethics in the counter-factual world where purely selfish behavior gives perfect utilitarian outcomes.
1Matt_Simpson
Indeed it does, but the two are not identical. See my response to Andrew above.
I think the last block of text is key.
If the ethicist's utility function is broad enough in scope to subsume (or at least recognize) that what is good for the economist is ultimately good for the rest of the system (if that were the case), then there might not necessarily be a need for distinction of utility functions.
It is possible the economist's utility function might hold some underlying (and unintentional) positive ethical effect.