Can you transfer a Windows 10 OEM licence to a VM while not running a Windows host OS?

In short; It will work, but is not allowed:

As stated on Microsoft.com:

You are required to support the license on that original PC, but you cannot support a license that has been moved from a PC that you manufactured to one that you did not. This is one of the key reasons why an OEM System Builder License can’t be transferred.​​​​​​​​​​​​​​​​​​

If you had a non OEM license it would have been OK to virtualize your Windows, so long as you deactivate the old one.

source: http://www.microsoft.com/OEM/en/licensing/sblicensing/Pages/transfer_oem_licenses.aspx