@Joshua, don't think so, for example:
We have a city at 10, all citizens but one unhappy 20 food is needed, 2 is served by the city itself and the 1 tile worked for say 2 food. -16 food. Now with settler production and happy citizens the surplus food they produce is used for production, unhappy citizens don't detract from the surplus as i'd expected they do, if the unhappy citizen would otherwise have worked a food neutral tile it doesn't matter one bit if he's happy working it or unhappy not working it for settler/worker production.
But in the unhappy case i sketched there's no surplus at all and there's just no food to keep the unhappy's alive. Sorry if this seems a bit vague, i'm struggling with this new concept a bit myself.