I've definitely seen this. This includes a handful of threads discussing legitimate concerns about BULLRUN-style influence that were suddenly insta-flagged, punted from the front page and hidden form the main index[1] by those same shills. Several times the "nothing to see here" explanation took the form of a sudden concern for "not wanting to tarnish someone's reputation".

[1] which means moderator access

edit:

Anybody that thinks this is unlikely needs to watch PHK's "Operation Orchestra":

https://archive.fosdem.org/2014/schedule/event/nsa_operation...