I've heard obligation on a certain percentage of recording dates, but it's hard to say. The Full Moon Ensemble was Delcloo's thing, and its initial incarnation with Arthur Jones, Jacques Coursil, Burton Greene and Beb sounded great. Delcloo's sense of space and colour is remarkable on those occasions. It's too bad the rest of his work pales in comparison (though Africanasia is pretty cool).
I'm wracking my brain trying to think of French free drummers active in Paris in 1969, and coming up with very little. Somehow I can't imagine Charles Saudrais or Daniel Humair, great as they are (even in a semi-out context), making a BYG date. So Delcloo might've been one of the few locals around then who could even halfway cut it.
PS - don't drag Beb down with Delcloo; he was around well before and well after the Actuel sessions, and made stellar contributions to a number of dates - Tusques, Portal, duos with Francois Mechali, etc.