JV Relatives uses meta keywords to put articles into relation. Custom Properties tags are database records. So both extensions can exist in the same installation, but they do not cooperate.
Joomla 2.5 has new means for searching: the so called "smart search". At the moment we have only limited knowledge of that feature, but looks promising and very "search-engine-esque", with typo detection, advanced search, natural language processing and indexing to analyze content and establish relevance.
There's also taxonomy (which differs from tagging).
Joomla 2.5 doesn't seem to offer native tagging.
So far we haven't seen Custom Properties most notable feature* built into J 2.5.
* Custom Properties is a Joomla! Extension for creating and assigning custom properties to articles and other content items. Using the CP search module, articles can be searched by combining more criteria.
