The guidelines for Exchange Server 2013 virtualization has been updated per 1. may, and as a new feature, it is now supported to deploy Exchange Server 2013 on Infrastructure-as-a-Service (IaaS) providers, like Microsoft Azure Virtual Machines.
Note that for Azure VMs, Exchange databases, transport and transaction logs must be placed on Azure Premium Storage.
Deployment of Exchange 2013 on Infrastructure-as-a-Service (IaaS) providers is supported if all supportability requirements are met. In the case of providers who are provisioning virtual machines, these requirements include ensuring that the hypervisor being used for Exchange virtual machines is fully supported, and that the infrastructure to be utilized by Exchange meets the performance requirements that were determined during the sizing process. Deployment on Microsoft Azure virtual machines is supported if all storage volumes used for Exchange databases and database transaction logs (including transport databases) are configured for Azure Premium Storage.
Guidelines for Exchange Server 2013 virtualization: https://technet.microsoft.com/en-us/library/jj619301%28v=exchg.150%29.aspx