For a search engine to see a post in Discourse it must be in an “everyone” has “read” permission category and the forum must not be “logged in required”.
This means that for search engines to be able to see it, forum members will also be able to see it. The only way around this would be to have some JavaScript code that hides a post from logged in users. Doing so is against webmaster guidelines and could result in a penalty.
If you post a “hot issue topic”, for example “Charlottesville”, that has nothing to do with the forum’s niche and was posted only for the purpose of getting traffic from searches, you run the risk of having people being disappointed that the forum has little to do with the post they clicked to. You may get page views, but it will do little to benefit the forums community as they will be unlikely to join it. You also run the risk of polluting the forums niche which could devalue its “authority”.