You don't need to get consent to boost a public post on Mastodon. If it's posted publicly on a platform that allows re-sharing, you can reshare it.

But that principle is strained nearly to the breaking point by auto-boosting everything in a given hashtag.

And trying to create accounts to become the public face of a given hashtag is something else again. That's deliberately harvesting attention that belongs to the hashtag and the people creating content under it.