With Blogger based comments, only the blog owner is allowed to report abusive comments published against their blog. You are free to classify or delete comments posted against your blog - but comments posted against somebody else's blog are their business, and their opinion. With Google+ based comments, moderation is a community exercise . Anybody, seeing an abusive Google+ hosted comment or post, is able to "Block" and / or "Report abuse". You, the blog owner, have no special responsibilities or rights , with regard to comments posted by someone else, against your blog.
What Blogger won't tell you