Using OS X Server as Virtual host as well as other things.

I am seriously contemplating the Mac Pro Server.

The reason is for development and I want to use it for the following:

The usual OS X Server features (iCal server, web server, email server....)
Ubuntu VM
Windows VM
Linux VM

I want to be able to distribute disk images when new machines are added to the network, test applications/ web sites on each version of an OS and browsers, create a staging and testing VM of the final web server and so on...

The question is, can OS X Lion/ Mountain Lion server do this natively or would I need to use VMWare, or would I be best buying an ESXi / Windows VM Server?