According to many sources on the Internet its possible to get GPU usage (load) using D3DKMTQueryStatistics.
How to query GPU Usage in DirectX?
I've succeded to get memory information using code from here with slight modifications: http://processhacker.sourceforge.net/forums/viewtopic.php?t=325#p1338
However I didn't find a member of D3DKMT_QUERYSTATISTICS structure that should carry information regarding GPU usage.