In the support matrix it says that Data ONTAP 8.1 support Windows 2012 with Hyper-v role.
In the documentation of 8.1 it says nothing about the LUN type that should be used for Windows 2012 Hyper-v, however in ONTAP 8.1.1 documentation it says that LUN type should be Windows_2008 if you are going to use Windows 2012 Hyper-v.
Is it the same case for ONTAP 8.1 ?
If instead of Windows_2008 we used hyper_v will it cause misalignment ?
There is no technical difference with the windows_2008 and hyper_v lun types. These are used primarily by SnapDrive. However yes you should use windows_2008 for any Server 2012 luns, and hyper_v for any hyper_v luns. This will ensure that all NetApp software recognizes the associated LUNs and handles them appropriately, but from an alignment point of view they are the same.