Can Launchbar tag files?
Tagging is supported since LaunchBar 6, released June 11, 2014.


You either send a file or a selection of files from Finder to LB
(alt + holding space) or select a file (or – with nightly build
6.1 – a selection of files) within LB.
Then press tab, type a part of the Finder tag name and add the tag 
by pressing return. You have also the option to replace existing tags with the new tag.


You can display a file’s tags by pressing → after selecting the file in LB.

LaunchBar 6.3 added support to work with multiple tags at once.