Pagination might not be the best approach for handling concurrency but it still is a good approach to use in any list page. Not allowing a user to browse between all items and showing them only a bunch in a fixed order will not allow the user to find a specific post without performing actions on the rest of them.
Particularly talking about the concurrency issue, I think it is not possible to remove it. However, it is possible to decrease it considerably. Apart from the browsing feature suggested before, there could be a "moderating mode" in which moderators would only see one post at a time and have the ability to operate on it or skip it, or whatever they want to do. That way, each post processed will update the server immediately and it will not give that post to other moderators performing the same task. This doesn't solve the issue because if there are more than one moderators at the same time operating in that section with only one pending post, both of them would be displayed the given post. It is not perfect but it is much better IMO.