Officially it is not supported, but unofficially I can tell you that it works with VMware Server 2.0 just fine
Personally, I am monitoring the VMware Server host running my test lab since day one. There are just a few minor issues with it (couple of less important graphs have data missing).
When adding VMware Server 2.0 to Veeam Monitor, keep in mind that VMware Server uses port which is different from the one ESX/VC are using. By default, it is 8333 - and you need to specify it when adding your server to the console. Other than that, no special tricks are needed to make it work.