We have a customer on our Cloud Platform (multi-tenanted) who have their own windows server Datacentre licenses. can they use their Datacentre Licenses on this platform if they inform Microsoft?

Since Windows Server is licensed based on "physical" cores on the physical host/server, the physical server hardware needs to be licensed and reported by the SPLA provider in a multi-tenanted or shared hardware environment. At this stage, Windows Server do not have any "license mobility through Software Assurance" right - I.e. the end customer cannot bring their Windows Server licenses to your shared hardware/multi-tenanted environment.

However, end-customer can bring their volume licenses to be hosted on a dedicated hardware. In this scenario, there are no requirement for active Software Assurance on customer’ licenses. Note that, from a Microsoft perspective, the term “dedicated” refers to the physical server hardware that is dedicated solely for the end-customer.