I really loved this guide, and a lot of it is consistent with what I've heard and read as well. I would agree with the people who have commented that including other peoples' channel names in your tags is sketchy. I would not necessarily say that YouTube can tell when you're doing it (because I don't think YouTube's system is that "smart" -- tag-based spam has to be detected manually rather than automatically.), but rather, it's unethical and misleading to potential viewers. I'd rather get into the suggested videos of other channels through shared content tags, rather than because I artificially created a connection by putting the other channel's name in my tags. I only include channel names in my tags if I've done a collaboration with the other person, or if I'm discussing the other person extensively.
Obviously, most people won't check tags on a video, but if I see a bunch of other channels' names in their tags through TubeBuddy, that gives me a bit of a worse impression of the youtuber.