For Microsoft customers with software assurance, Azure HUB allows you to use on-premises Windows Server and SQL licenses and run workloads such as a VM or Microsoft SQL Server on Azure at a reduced cost. Azure HUB can be used for Windows Server or Microsoft SQL to deploy new VMs with Windows OS or SQL Server.
Looking at Windows Server, you get the following offering when using HUB.
Each two-processor license or each set of 16-core licenses can be used with two instances of up to eight cores, or one instance of up to 16 cores. The Azure Hybrid Benefit for Standard Edition licenses can either be used on-premises or in Azure. The Datacenter Edition benefits allow for simultaneous use on-premises and in Azure.
Currently, there is no automated tracking of HUB licenses in Azure or in any offering, such as Key Management Service (KMS) or Active Directory (AD) based license activation. So, you need to track their usage by yourself to be prepared for a license...