Q: Is it OK to create a Hyper-V virtual machine (VM) with an odd number of virtual processors?
A: A VM can have between 1 and 64 virtual CPUs in Windows Server 2012 and later. Typically, VMs are given 1, 2, 4, 8 and so on virtual processors. This matches many physical server configurations.
Although 1 is an odd number, it's not common to see a VM with 3 or 5 virtual CPUs. However, there is nothing to stop you from doing that. Hyper-V and Windows itself have no problem with an odd number of processors, and there's no need to have an even number.