I think all of the ACM conferences I contribute to have stopped actually printing physical proceedings. The consistent formatting is by a LaTeX document class, with an automated system that checks for bad fonts, text going into the margin, etc. The PDF that ends up in the Digital Library is the one the author submits (possibly with a watermark or stamp applied). I don't know if there is a small amount of ACM-provided human labour employed somewhere, but mostly they just provide a small amount of automation.