The CGI movies of the Witcher series are made by Platige Images in Poland and have nothing to do with the RedEngine or Redkit. The ingame cutscenes, etc. are made with a program called Motion Builder and then imported into Redkit.
So I guess it would be possible to make movies like those in Redkit, but you would need this program.
You don't need motion builder at all to make cutscenes in game, all you need is a 3D program and/or 3Ds Max version 9, 2008 or 2009, Maya 8, 8.5, 2008 and 2009. XSI 6.0, 6.5 and 7.0 with the Havok Content Tools installed (The version should be 6.5.0). Then you simply just need to know how to import and use the animations. As of know until they make their own exporter that supports animations.