It is a known fact that gallowboob will repeatedly repost and delete something over and over while deleting competing posts until his gains traction

They can pin posts to the top of the subreddit though can’t they? I have to imagine that increases post traffic/upvotes/interaction.

Yes, but I've never seen this done for normal posts, just rule announcements and such.

Speaking from experience as a Redditor and Reddit mod, it does happen - just some subs are more diligent about avoiding shills than others.

Huh, I have the same experience and we never did it on my subreddits (and I rarely saw it, but I usually browse /r/all)...