Report them to twitter and to bounty manager.
If the advertiser is getting the exposure they are paying for this should not be an issue.
Does it apply to bitcointalk too?
If advertiser is getting the exposure bots and spam shouldn't be problem? I don't think so. It shouldn't be different with twitter or any other social media.
The appropriate response to someone using a bot to spam on bitcointalk is to ban them, assuming the posts are breaking forum rules.
There are a couple of bots running around here that some may be interested in advertising in their sig space. If someone can develop an AI bot that is smart enough to post intelligently, a reasonable person not on a power trip will not have an issue with this.