Bots on Reddit for example did farm karma to later sell those accounts (more karma makes accounts look more legit) or circumnavigate karma thresholds to spam. There is no karma here so that's (hopefully) not going to become a thing.

I see no reason why they couldn't. There's even built-in support for bots in the user settings, at least in Lemmy.

Like on Reddit, it will take some moderation to keep the more malicious bots under control in the Fediverse.

I'm not informed on the topic by any means, but my take is reddit should be less susceptible because they have the resources to combat bots and spam -- or at least empower mods to do so -- but they choose not to. It's pretty surprising to me that they cut support for critical mod tools like Pushshift without having a replacement ready to go. The mod support posts only spoke of tools/capabilities they were planning or committing to, or links to "we want to help" pages. Lemmy is probably more susceptible to bots, especially now, but I think a lot of that up-to-date expertise of how to spot bots is coming over with the new wave of membership. Plus, I don't know if or how bots would be worth it here aside from trolling.

tl;dr I have no idea