When you convert an AI file in PS to PDF does it always flatten everything and rasterize it? If it doesn't does it flatten it or rasterize before it goes to print?
Open the pdf back in Illustrator and that is what is being sent to postscript printers.
Smart objects, text & shapes from Photoshop get bitmapped (with bleed), but they get put in a mask so they have a vector edge.
If you open the same pdf back in Photoshop, and had preserve Photshop editing on, then you will get text and shapes, smart objects back.
In my reseach fo this in the past, you get what you see in Illustrator, as smart objects get bitmapped (at the resolution of your file which for the majority in print is 300 dpi) and don't have a vector resolution.