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.
I personally wouldn't see this is as a problem at all, using a program/script/bot to post a tweet on a regular schedule does not affect the bounty or anyone. People can upload videos on youtube automatically on a schdeule for instance. As long as it's not spam, which it isn't, it's fine.