Tags have always gone along with shared posts, except during a glitch a year or so ago and back in the beginning, posts were searchable from the shared-to Kinja blog, but I don't believe that's been the case since the glitch. Right now, Kinja only searches posts sourced on the blog which initiated the search.
As regular Kinja users, it's not a big deal for those of us in the user-generated communities to work around this lack of functionality. Sometimes it would be easier if shared posts were indexed from the target blog, but you can always find posts with a full Kinja search and the biggest difficulty I've found is when searching to see if a subject had been previously shared.
Casual readers of the Gawker blogs aren't as familiar with the Kinja platform, so when they run a search from the Gawker homepage, they probably don't realize that the results aren't going to include anything published to justice. or tktk.gawker, whether or not it was shared to the Gawker homepage. They might remember that they saw a post on Gawker Main, but if it wasn't published directly to it, it's not going to come up in a search and the only way to see if there has been any Gawker coverage of a particular subject is to run a full Kinja search, use an outside search engine or search each subdomain individually.
On a semi-related note, if they decide to stick with this scheme, they might need to do something different with tags. At this time it's pretty obvious that each of the new Gawker sub's tags begin on the day they were created, but in the future, it's not going to be as clear that to find all of Gawker's coverage of a particular subject, a person would need to access the tags from both the subs and Gawker Main. Adding to the confusion will be the fact that because tags follow on shared posts, there will be some duplication on the most recent results.
(I've tagged this Kinja-Help as an FYI, in case this effect hadn't been realized)