Like how tamaryuu and 玉竜 have different artist pages with different info, despite 玉竜 being an alias of tamaryuu, being referred to as such on the artist page, and being properly aliased as such in the posts section itself.

Good question. Presumably the artist page and tags/aliases were written at different times and had different intentions. The artist pages are more an extension of the wiki than anything (if you'll notice, the "Notes" field actually just edits the wiki page) which also doesn't take aliases into account aside from the text at the bottom ("The following tags are aliased to this tag"). I suspect it hasn't been done yet because there's no real way to handle conflicting/duplicate data (transferring wikis, different e6 user IDs, etc.).

It's a good idea though. I'll make note of it and pass it onto our devs. I'd also recommend you post this to the Feature Request Thread as it's something the devs look at on a regular basis and it will help it from getting lost.