The conceit may be strange, but one performer’s energy can make all the difference. In Daniel Beaty’s show, Emergence-See!, now being performed at Arena Stage, a slave ship has shown up in a modern-day New York harbor. Protagonist Rodney’s father’s headed right towards it, as it’s messing up the poetry slam in which he’s supposed to be performing. A little farfetched? Truly. But Emergence-See! isn’t a show that is dependent on its set-up. It’s one…