Rob – the details of a separated workflow are completely outside the PDF/X specification (and the PDF spec, for that matter). Acrobat assumes a modern composite and/or digital workflow, where the PDF/X file will be processed by a native PDF RIP according to the rules of PDF/X (rather than a historical separated Postscript workflow).
Neither InDesign nor Photoshop support PDF/X-compliant rendering, so the point is moot.
