>>1320
When you say 'access to its tagging system', what do you mean? Do you mean downloading gelbooru's tags and associating them with the files in your hydrus client?
You can get tags while you download files through the hydrus booru downloader page, but just 'getting tags for my files' can be technically tricky. Gathering and sharing tags for files is a difficult problem, and one of the main reasons why I made hydrus!
Lots of gelbooru's files are tagged on my public tag repository, so syncing with that is a good start.
You can also try syncronising with the gelbooru tag archive, which is a little old now but has a lot of gelbooru's tags:
http://www.mediafire.com/download/rvjekisb3pan9wa/gelbooru.7z
There is a short guide on tag archives here:
http://hydrusnetwork.github.io/hydrus/help/advanced.html
Just scroll down a bit.
Let me know if you would like any help with any of that, or if I misunderstood your question.