We already have a yammer tag, with five questions. So fire away - ask your yammer questions, as long as they are related to SharePoint. Otherwise, you'd have better chances at the yammer forums you mention.
SharePoint and Yammer seems to be more and more merged together in what Microsoft refer to as their "Social Layer" that will span most of their products.
To me I would therefore gladly see questions about Yammer posted here on SP.SE, it is surely within the scope of the community and I bet that many of out members has valuable knowledge regarding it :)
Check boxes are going to act just like tags and be just as useless. Years and versions are too broad to properly tag a question.
If I pose a question about WCM and tag it sharepoint enterprise, that does nothing for the visibility of the question. If I tag it what it is, WCM, then it immediately becomes apparent what the question is about.
Years and ...
As you already pointed out, 3rd party applications are off topic for this site. These applications already have their own support channels, and you are supposed to use them. This is especially true for payed for applications like the ones you mention in your question.
Free Open Source 3rd party applications also falls into the same category, but some of ...