Romulan ale should be illegal. Nemesisseems to provoke the most outrage among fans the reasons mostly appearing to boil down to continuity and character work. This implies that what is actually illegal would be trading with the romulans in defiance of this embargo not necessarily actually possessing romulan ale as with cuban cigars in the us. In the case of the former while i can appreciate the beef im not enough of an aficionado to get too worked up.
Presumably starfleet officers skirt the embargo by trading with the romulans indirectly. At the wedding of riker and troi worf has too much of it and notes that it should be illegal and geordi replies it is even in star trek. Picard soji and narek shared a bottle.