I don't think there is any tag/topic and metadata integration between Yammer and SharePoint.
What's your hypothetical use case? You certainly could create a Topic in Yammer that's named after a specific SharePoint site (e.g. your company portal if it has a specific "name"), but you wouldn't be able to click the topic to open a tab into the SharePoint site.
Many years ago I designed an Intranet with a Yammer button at the bottom. Clicking on the button showed all conversations linked to that specific page and all the conversations were stored in the same public Intranet group as we automatically changed the default Yammer group for the posts. This made it very easy for users to provide feedback on the different pages of the Intranet and it made sure that users could see feedback from others before sharing feedback themselves. Sharing links to external websites or SharePoint pages creates an object in Yammer and that's the feature we used for this. Had to rely on a developer from my team to actually realize this and I'm not sure if this would be useful for your use case.