A documentation SIG is not really Wikimedia-specific though (or did you mean "ORES documentation SIG" specifically?).

Also, most Wikimedia-specific technology initiatives are on mw.org (all the Audiences projects, for example).

Wikitech was originally a place for ops documentation. (It has its own infrastructure and deploy cadence, so it's unaffected by most failures; also it's small enough for static HTML dumps. When the site is down and you are scrambling to bring it back, it's a good thing when your operations docs aren't also down.) Later Labs needed a management interface which got tucked onto Wikitech (this was one of those "do everything inside MediaWiki" eras), so it made sense to put all Labs-related documentation on wikitech as well. Most other things are on mediawiki.org. There were various proposals over the years to change that (move wikitech content to mediawiki.org, move all WMF stuff to wikitech, move all WMF stuff to meta, move all non-MediaWiki-documentation stuff to a new developer wiki etc.) but none of them gained much momentum.

Due to being managed differently, wikitech is not a great work environment IMO. There is no unified login, no page translation support, no structured discussion support, no pageview metrics, the registration process is tied to creating LDAP and shell accounts... There are plans to improve this eventually [1], but between that and the audience differences, I'd stay away for now.

Btw you are probably aware of the past discussion on a documentation SIG, but just in case: [2]

[1] https://phabricator.wikimedia.org/T123425

[2] https://phabricator.wikimedia.org/T156301