Sorry it took me a while to respond, got a little occupied IRL!
From what I've seen, it does seem like quite a few devs I follow do upload incomplete games far before they're even in a playable early access state. These early entries tend to be associated with ongoing Jams from what I've seen, and updates posted to them serve to make said games' devlogs publicly accessible. I don't know how many people read said entries, but I do know that a few developers frequently post progress updates, even if they don't yet have a demo to show for their work.
So in the long run, it's less about "itch.io" culture from what I can tell, and more about "each individual dev's culture." Some developers' updates are just links to external sites (blog spots, tumblrs, forum threads, Ludum Dare pages), others' are just announcing that the version on itch has been updated or patched and posting a snippet of a changelog, some are screenshots or videos, others are Patreon links and inventive listings, etc. There doesn't really seem to be a standard people follow- plenty of developers just upload their new game and only really interact on their game page's comments, others only participate in jams exclusively and only post within the forum of a jam they're currently working on.
At any rate, I think you should just choose something you're comfortable with! Since the site hosts pen and paper modules, comics, and tools as well and all of these can have "devlogs" of sorts made for each, it's kind of difficult to really cement a sitewide culture.