Defragmenting SQL Server data and log files live with MoveFile API
Personally, I wouldn't want any antivirus or defrag software anywhere near a database file. Ask yourself, is this going to cause more problems than it's going to solve? 

From A tale of CHECKDB failures cause by 3rd party file-system drivers:


  At the end of last week, Diskeeper 2009 was upgraded to Diskeeper 2010
  on the servers by our server team.  Diskeeper 2009 had been there for
  at least a year without problems so who would have expected it to be
  the issue.  Turns out the new version has an option enabled called
  IntelliWrite that causes this problem to occur.  Disabling this option
  immediately resolve the problem.  Paul blogged about this problem a
  long time ago, and recalled reading this when I clicked on it but it
  was the last thing that I would have thought about.


From Beware 3rd party file-system drivers with DBCC CHECKDB


  I don't want to cry 'wolf' here, but be careful of attributing massive
  corruption problems to the real IO subsystem if there's any kind of
  file-system filter driver installed.


With proper planning and management, you shouldn't need to defrag your database files.