The tags are not available as a field in the seedlist, and therefore the text in the tags is not searchable out-of-the-box.
In order to make them searchable you need to follow this undocumented trick:
On a recent project we learned the hard way that the Remote Search server needed a restart too so that this takes affect. If you do not restart the remote search server then you will see the tag field in your seedlist and search results xml but those fields will not actually be searched.
You can use tagging to promote content for your search since the tag field seems to be processed using a higher relevance than other fields.