I don't believe it treats it any differently. In other words, it will
find the AD object  and update it.

Also keep in mind, that before Portal will mark the profile  for
deletion, it has to complete 3 consectutive "FULL" crawls of the profile
database, and any incremental crawl will reset that counter. This is
slightly different than crawling other data, where an incremental does
not restart the 3 strikes and you're out counter.