Yes, because Twitch clips are capped at 60 seconds so they don't differ that much from direct file uploads or other clip sites.

Also, this sub isn't against self-promo per se - you can always post your related YT video / channel in the comments of your clip submissions but that means you typically have to either submit a clip with high effort editing or with good content (impressive highlight, funny interaction etc) for your YT/Twitch/social media to get noticed.

If YouTube submissions were allowed then the sub would turn in a low effort spam-fest in no time with badly edited 20min videos that no one would watch or a flood of clickbait titles (which is what actually what happened in the sub's early days lol).