The Party was embarrassed by Picasso's jaunty drawing of Stalin for his birthday, but he stayed in the party.
Breton collaborated with Trotsky on a pamphlet.
Dali's fascism was a pose, most likely an expression of his irritation at the pious leftism of his formerly iconoclastic fellows. He once insisted on greeting Franco on a visit to his home town, and arrived, elderly, dressed in a militaristic uniform of his own concoction with mdeals epaulettes, ostrich feathers and a sword. Unfortunately, the grand old man of surrealism bowed so low before Franco that he could not get up again, much to the embarrassment of the General, who wondered who the lunatic blocking his way was.
Many surrealists organised in a fashion that was hard to distinguish from underground Trotskyist and anarchist groups - see the excellent biog. of Guy Debord The Game of War.
My father knew many of the Surrealists in Britain in the 1950s, Conroy Maddox, Anthony Earnshaw and Arthur Moyse - the last two were anarchists, supporters of the group Freedom, I think. Earnshaw was scathing of Marxism and used to tell me 'You've backed the wrong 'orse'.
The avant garde musician Cornelius Cardew was senior in the Maoist Revolutionary Communist Party of Britain (Marxist Leninist) and wrote a funny pamphlet called Stockhausen Serves Imperialism (but probably wasn't assassinated, as his group's paper alleged when he was run down in the snow). John Tilbury has just written a biography.
Marcel Marien was sceptical of the Belgian Resistance poets, and said 'ah yes, the Belgian resistance: that was after the war'.