It would certainly be nice to get some details on this, so that we have something to look at—particularly given a lack of direct testing ability in InDesign.
I would also cast my vote in for the advice given in this post, above. Switching to a Pandoc-based DOCX output is perhaps not as much of an upheaval as you might think, given how Scrivener augments and supports Markdown so well. It is quite possible to not use any Markdown in your text, and indeed that means a project that already doesn’t have any can be made to work with it.
The main dependency on Scrivener’s side, I would say, is effective style usage. If you’re working closely to the start of the publication process as it sounds, then you might already be in a good place for that.
Here is a quickstart guide on Pandoc+Scrivener, which I think is the best place to cover both the basic idea, and provide a checklist of steps to follow to try it out. It was written specifically for those looking to add an index, which Scrivener’s basic output of course cannot do, but has built-in presets for doing with this alternative way of compiling.
Otherwise, maybe check around here for threads on InDesign. There have in the past been publishers on this forum that have posted how they use Scrivener with it. If it is as dire and unworkable as your colleague states, it seems we would have heard something from these posters, or any of the many more amateur and hobbyist designers that have posted their successes, too.