In 1988, Madison Square Garden welcomed an all-star lineup for a show that benefitted Greenpeace and the Rainforest Action Center headlined by acts like the Grateful Dead and Hall & Oates. And the two collaborated later in the evening during the Dead’s second set. Daryl Hall and John Oates, then two of the biggest musicians on the planet, teamed with the Dead for a cover of Marvin Gaye’s…