It could be like trying to find a needle in a haystack, the differences between the two hypervisors are many from the little I have read about the hypervisor in UnRaid.
I see a few things that jump out, maybe they are nothing...
<vmtemplate name="Custom" icon="windows98.png" os="windowsxp"/> Why windows XP?
<type arch='x86_64' machine='pc-i440fx-2.3'>hvm</type> Windows 98 was 16 bit, XP came in 32 and 64 bit versions.. not sure if this matters.
Im am familiar with virtualization and VMWare, just not the hypervisor in UnRaid, so sorry I can't be of anymore help.