Is pecorino cheese suitable for vegetarians?

Unfortunately, not usually. You have to ask because more than 90 percent of the time Pecorino is made with calf rennet. Don't trust the label unless it says explicitly Pecorino con caglio vegetale.
according to a cheese manufacturer (Pinzani's pecorinos) website this is what they say about pecorino...

warm milk is made to coagulate by the addition of an enzyme, the rennet (animal rennet or vegetable rennet )

they make a vegetarian version called Pecorino con caglio vegetale

so the quick answer is yes and no! if in doubt ask the restuarant or shop