Indeed they can, and it is a remarkably good pairing of two tools, each with their distinct strengths and very little functional overlap, without pushing either tool into an arena it wasn’t designed for. A very simple way of doing so is to designate an area of your binder for notes with the external folder sync feature, and then opening the entire sync folder as a vault in Obsidian. Put the two programs side by side on the screen, and now you can use it as a “front end” for your notes, which all go straight back into the binder where they can be organised and interlinked with the drafting process in the Draft folder. You get the best of both worlds without the posturing over which is “better”.
For those with one foot (or two) already in the Markdown pool, it’s certainly worth looking into, if you’ve been wanting something a bit more like a “notepad” interface that integrates more deeply with Markdown directly than Scrivener does.
While these two posts focus on integrating with Ulysses and Sublime Text, the underlying concepts from Scrivener’s side are identical to integrating with Obsidian, Visual Studio Code, Vim and hundreds of other file-system based tools:
There are large and critical chunks of how I use Scrivener that would be flat out impossible to bring to iOS, simply because Apple does not allow that kind of software to be published through their locked down store, nor provide any development tools for doing so in the first place. To put it another way: to actually port the full power of the desktop “app” to iOS you’d have to first jailbreak it and install Linux.
So overall this type of argument is not very compelling to me, and secondly I would also question its veracity, since off of the top of my head I can think of a several things Obsidian on desktop can do that iOS wouldn’t allow. We’re talking about one of them in fact.