more examples of writers/activists combination...

Nazim Hikmet--Turkish writer; one of few writers to speak out against Armenian genocide.

Ernesto Cardenal--Nicaraguan poet; latin america has lots of examples of poets who do activist work; also Rigoberto López Pérez--Nicaraguan poet who killed Somoza

more closer to home, I think this project by Sarah Schulman, novelist, where she is interviewing all the members of actup ny and archiving it on the web at http://www.actuporalhistory.org is a good example of the intersection between art and activism.