Yes, that's actually fairly common. Just yesterday I had an encounter with one: /u/speaksthetruthalways (now shadowbanned for vote manipulation along with many of his alternate accounts). He would post comments regarding many groups, including women, LGBT people, and foreigners. Its clear from his posting habits he is a rather far-right, socially conservative, anti-immigrant European, but was really telling was the way he worded his comments. If a title or comment so much as mentioned a group of people he had a problem with (usually immigrants) he would post a link to a video or a picture that painted that group in a bad light, and nothing else, and it often wouldn't make sense in context. Or, even more telling, he would post nonsense Red Pill, PolFact, or Stormfront copypasta if a comment so much as mentioned the word "women" or "immigrant." But nevertheless these nearly worthless and barely relevant comments were often upvoted and even gilded, despite being completely unsubtle attempts at bigoted fear-mongering and xenophobia. When I called him out on it on doing this in countless threads, I was steadily upvoted. However, after he saw my comment and replied to me personally (later deleting his reply), my comments were quickly downvoted below the threshold, and previously unseen accounts replied to me and tried to discredit me. "Well YOURE racist if you think his completely 100% true, unbiased, and relevant comment is racist or political in nature!" Clearly using a multitude of his accounts and fellow brigading anti-immigrant folks to hide my comments. I eventually stopped commenting for a little while, since he seemed to be using his accounts to downvote all my comments in my history.

Once he stopped, I told everyone to report him for vote manipulation and linked evidence that another user had gathered of several accounts he used that were his alts. Scumbag would use dozens of accounts to "nudge" his comments up ever so slightly and downvoted all the others several times (but not too many to garner suspicion), or even to set up conversations that tried to discredit whatever he had a hate-boner for at the time. He would even gild his own posts, several times, to give an image of "truthfulness" and respectability to his comment, making it more likely to be upvoted. Once it was in the +15-20 range, it would enter "rising" and there would then be a good chance it would outshine other, more relevant comments and be upvoted by people who came to the thread early and shared his views. In more extreme cases he most likely linked the comment to right-wing subreddits for brigading.

That evidence proved more than enough for the admins to ban him and all of his known alternate accounts. I had seen this guy spewing his nonsense, irrelevant comments on half the post on /r/all, and now I finally knew how that junk got upvoted. Glad his shitposting is done for, but I was blown away by how long he managed to do that for on the front page without getting called out. If you're interested in this whole mess my comments from that thread are close to the top of my post history.