the pro-blogger functionality is not just a 'tag' to differentiate the pro-blogger from a regular blogger. It adds functionality: a pro-blogger has e.g. his own profile page where a blogger doesn't.
We also have other 'tags' based on the 'authority' of the blogger: a tag can be assigned based on the number of blogs [blogger badges], the number of views [Influencer badges], etc. These are dynamic tags that are an incentive for bloggers to blog more / better
The a blog itself can also have tags, tags assigned on number of hits on the blogs. these add value to the visitor as a blog labeled as top-blog must be worth reading
That said, there is currently no functionality where tags are added based on a blogger his group membership, but that could be implemented, in the same way we currently implement e.g. the blogger badges:
[group id],[displayed badge name],[css label]