You cannot place your own customer hardware in the Microsoft Datacenters. The intent of the Windows Azure Virtual Network is to allow the cloud hosted software based side of the VN to connect to an onsite VPN (either hardware or software).
So for some of your partners, you could connect Azure to their existing hardware based VPN devices in their own datacenters, or that you are hosting for them in yours.
Note that currently, a Virtual Network is limited to connecting to a single VPN gateway. So "multi-tenant" solutions that require individual VPN gateways for each tenant are not readily supported without some type of intermediary/proxy.