In MDT 2012 RTW that released back in April, we included support for DaRT 7, making it easy to add the DaRT components to Lite Touch boot images. See http://blogs.technet.com/b/mniehaus/archive/2011/11/28/mdt-2012-new-feature-dart-integration.aspx for more details on that.
With MDT 2012 Update 1 Beta 1, we added support for DaRT 8 Beta, while leaving support for DaRT 7 too. So if you are using Windows AIK, you would use DaRT 7; when you are using Windows ADK, you would use DaRT 8. (In general, DaRT releases are OS-specific, so DaRT 8 is for Windows 8 and DaRT 7 is for Windows 7.)
The basic functionality with DaRT 8 is the same as with DaRT 7: we add all the tools to the boot image, and we automatically run the remote agent so that you can make remote connections into Windows PE using the remote viewer (which is integrated into the MDT monitoring solution). Additional functionality in MDT 2012 Update 1:
See http://windowsteamblog.com/windows/b/springboard/archive/2012/03/28/microsoft-dart-8-beta-q-amp-a.aspx for more information on DaRT 8.