Many have copied the rules and format of other bounty threads and changed few words here and there. I don't think it can be considered Plagiarism as it's just the rules that are the same while if the main ANN is copied, that's plagiarism which isn't the case here. They just need to add a disclaimer down to credit the original content creator.
Unless you've asked for permission for content written by someone else, then it most certainly is plagiarism. You can avoid *problems*, without asking the other party, by at least including the source. Whether this is worth a negative rating or not is debatable, but an optimal resolution could be reached if the relevant parties just sort it out themselves. I would also like to remind you of a case of similar plagiarism, where Lutpin tagged GirlBTC for stealing his work.