I don't know,,, According to guidelines, you are not allowed to do giveaways that will boost the number of your subscribers which makes no sense since
@OldManTenno did that type of giveaway, got reviewed and accepted in the Partner Program. Normally his giveaway will be a red flag for youtube to reject his channel!
Here's the source: productforums.google.com/forum/#!topic/youtube/NR-IurOqCvM;context-place=topicsearchin/youtube/giveaway$20questions
Funny thing is that I sent a message to Gleam.io and they told me everything they do complies with YouTube
Not sure if in the next Review OldManTenno will be safe or the people who reviewed his channel didn't pay attention to that. We can just speculate but it's kind of annoying that "rules" only apply to some channels and not others. I believe YouTube closed some channels for doing giveaways!