I have experience the same issue, with the flowing setup:
NVidia Grid K1
Citrix XenServer 6.5
Citrix XenApp 6.0 (Windows 2008 R2)
NVidia vGPU Drivers for XenServer 6.5 - Windows Display Driver (341.08) and GRID vGPU Manager (340.57)
I manage to change the Windows Display Driver with 347.52-quadro-tesla-grid-winserv2008-2008r2-2012-64bit-international-whql.exe. After that, I do not get fault errors in nvoglv64.dll.