The States of Jersey opened a tourist office in Downtown Metropolitan Caen, and the service opened to coincide with that and lasted just as long as the tourist office. That suggests to me that there may have been a financial arrangement between the States and Aurigny - but that is purely conjecture on my part - I have absolutely no knowledge of any such arrangement.
During the time that there were flights to Cherbourg from the Islands, I never once saw any advertising in the local French papers in the Cotentin. However, La Presse de la Manche and Ouest France both carried prominent frequent advertising for the Caen - Jersey link. Make what you will of that . . .