Vanessa Williamsperformed at the Martha’s Vineyard Performing Arts Center on Saturday, accompanied by SiriusXM Radio host Seth Rudetsky, who played the piano and emceed the evening of songs and conversation.Their appearance was part of Mark Cortale’s inaugural Broadway concert series on the Vineyard, which continues July 16 with a performance by Megan Hilty.Rudetsky will return to fill the dual roles of host and pianist. Among those who said hello to Williams backstage was Matilda Cuomo, the widow of former New York governor Mario Cuomo.