Did Grothendieck acknowledge his collaborators' intellectual contributions?

1) I had begun writing a long answer but I found that analysing the thousand page paranoid rant "Récoltes et Semailles" too depressing.

2) Summing-up: the scandalous calumnies and accusations of plagiarism of Grothendieck toward mathematicians like Deligne, Illusie, Kashiwara, Kawai, Serre and many others would be unforgivable if it weren't for the tragic circumastances of Grothendieck's youth, who had to hide as a child in order not be murdered in Auschwitz like his father.

3) As to the actual question: Grothendieck is undoubtedly one of the greatest mathematicians of all times and his extraordinary creations and prophetic visions attracted some of the best mathematicians on earth to his seminars between 1955 and 1970 (roughly).
These mathematicians profited immensely from Grothendieck's genius, but the converse is also true.
Mike Artin made great contributions to étale cohomology and Demazure, Illusie, Oort, Hartshorne, Manin, Mumford, Murre, Raynaud, Verdier,... had many profound and creative insights which I can't go into for lack of space and above all competence.
Grothendieck apparently couldn't/wouldn't write down his mathematics and the thousands of pages we can read about his oeuvre are the result of the dedication of his volunteer scribes.
In the same vein, the prenotes to Part V of EGA show what EGA would have become without Dieudonné's heroic efforts to clean up the preliminary manuscripts of Grothendieck.
In conclusion, Grothendieck certainly gave a vital impulsion to the renewal of algebraic geometry in the late 50's and 60's, but that field has flowered thanks to the collaborative creativity of incredibly talented young (at the time) mathematicians, none of whom can be dismissed in Grothendieck's scornful way.

As a complement to George's (1), I would say that if you dig in the indeed depressing Récoltes et semailles you'll find severe hints towards a huge author's paranoïa (implying that one has to be cautious about taking for granted everything that is written there) and a profound respect for mainly three people :

• Jean-Pierre Serre (called a "detonator" for Grothendieck's ideas, mainly through their long correspondance)
• Pierre Deligne (for instance "Deligne avait été un peu élève de Tits (en Belgique) - je doute qu’il ait été élève de quelqu’un en mathématique, au sens courant du terme", or "Mon rôle mathématique auprès de Deligne s’est borné à le mettre au courant, à la petite semaine, du peu que je savais en géométrie algébrique, qu’il a appris comme on écoute un conte - comme s’il l’avait toujours su ; et chemin faisant aussi, à soulever des questions auxquelles le plus souvent il trouvait réponse, sur le champ ou dans les jours suivants")
• Zoghman Mebkhout (for whom the respect is quite tainted with pity, especially because Grothendieck blames him for having indulged his own "victim" condition)

I feel that Grothendieck had even more, way more, respect for Deligne than he had for Serre, which explains why he coined Deligne "principal master of the ceremony of the burial of Grothendieck's ideas" in Récoltes et semailles and why so much hatred and disappointment is felt from Grothendieck about him, and why so much obsession with him emanates from this book.