Can an Atlantic hurricane enter Mediterranean sea?
Apart from the fact that only a few tropical cyclones follow a more southerly route (a list bellow) after going around the North Atlantic, I think the main problem is that tropical cyclones would weaken significantly after landfall in the Iberian Peninsula. An example of this is Hurricane Raphael in 2012.
 Source Weather.unisys.com.

There is no "easy" path from the Atlantic into the Mediterranean for a system the size of a tropical cyclone. Other examples that followed a similar path but never made it the Mediterranean: Gordon (2006), Jeanne (1998), Ivan (1998), Frances (1992), Bob (1991), Arlene (1987), Chloe (1967), Carol (1965), Dolly (1953).

While the cyclones at the point of approaching the Iberian Peninsula are still tracked as tropical depressions, their characteristics are often similar to other extra-tropical storms.