Well, they would actually need to be interesting. There have been users who do what amounts to "interesting article arbitrage" by automatically submitting popular posts from other platforms.

You can find the submission guidelines here (https://news.ycombinator.com/newsguidelines.html). The only one that really would apply to a bot, anymore than a normal person, is "Please don't submit so many links at once that the new page is dominated by your submissions.", which naive bots are likely to do.

Yes, I would say so. Nobody is going to complain (at least not with a valid complaint) as long as the articles are perceived as interesting and upvoted. In fact, I imagine you could do a good Show HN about the bot if it worked well enough.

The problem is when the quality slips, and it starts sliding towards spam (even if the intention was good).

Seriously, though, do you have any evidence that this guy is a bot?