It is an honour (trust) system - just like Hybrid Use Benefit; they are based on the users logging into the workload - https://azure.microsoft.com/pricing/details/virtual-desktop/?WT.mc_id=AZ-MVP-5004796.
If you have the relevant user license, you are licensed for accessing that or multiple virtual machines.
There is no checking of the licenses by Azure - but if raising a support case, or a Microsoft review comes around, you may not be supported, or will have to pay additional funds to become compliant.
Rather, than a product based restriction - its process and terms and condition based: https://www.microsoft.com/licensing/terms/product/changes/all