I would encourage the community here to collaborate in regard to this matter. From our end it is important to mention that XenServer is a server OS that is not validated for NUC solutions. You can try it and it may work but we do not guarantee the correct functionality of it.
I believe the NIC drivers on the NUC6i5SYH are not compatible with XenServer 6.5 and below. However, with the recent release of XenServer 7, you should be able to install without any issues at all.