Here's A Pic From a 1980 Cherubini H36
The attached pic may give you an idea what the raised area looks like (this from a 1980 Cherubini Hunter 36).
Even without a raised area, it doesn't do any harm to drill as others have suggested a (say 1/8") pilot hole in the same area where my raised section is (its the same on both port and starboard on my boat). Its still possible that Hunter put in an aluminum plate without raising the area. There is an appx 1/4"-3/8" void space between the deck fiberglass and the inner liner for an aluminum plate to fit. If you don't find the aluminum, simply fill the exploration hole with epoxy being careful to be neat. Then a little white paint and no one will ever notice.
If you don't have almuminum, maybe others can chime in on this variation: The fiberglass on the cabin top is likely to be at least 1/4". Lots of fittings are screwed into just plain fiberglass. A winch usually has 5 mounting screws = lots of holding power. As long as the winch is used only to hoist the sail and one doesn't crank the tension really hard (use a short lenght winch handle), I would think that a winch would hold just fine without a backing plate?