Gratuity is a funny word if it is a mandatory charge. Service charges are required by law in France in restaurants. Such a hotel must be considered a restaurant if it is serving dinner and so would have the legal service charges added to the charges already, I would presume. Any bill in France is supposed to tell you that, though, it says right on the bill if it includes service or not (usually at the bottom or something). It will say "service compris" if it is included. Otherwise, it says service non compris. I have never seen that as legally it is supposed to be included in prices in all cases I know of or have encountered.

So look at what you agreed to, it might say. If not, assume it does (in fact, I think a lot of inns with "half board" options may not state the service issue on their price lists, but some do).

Here is an example of a 4* hotel in Cassis that clearly states service is included, that's what I would expect:
http://www.roches-blanches-cassis.com/uk/index.php#tarifs-et-offres-speciales.php

If you are calling a gratuity something other than a service charge, it's really up to you what you give people money for. But if you give people extra money for things because you like to be generous or something, that would never be included in a mandatory price on a bill, by definition.

No tip is necessary or even expected. However, nobody will refuse a tip if you think they deserve one. In France, this is generally 5% or much less. (For example at a normal restaurant or for a taxi ride, this just means rounding up payment to the next euro.) Employees in France receive normal wages and do not need to beg to give proper service.