We have a test system where a VirtualBox VM snapshot is started before each major test. The snapshot contains a state of the tested system specific to the test.
This is a memory-intensive testing.
There is an idea to move the daily test run into Amazon EC2 Large instance (7.5G of RAM).
My understanding though is that EC2 is a supervisor itself. Will it allow another VM software (VirtualBox) to get started under it?
Well, Amazon now allows to import VirtualBox and VMWare VMs. Not all operation systems are supported yet, but they work on it:
http://aws.amazon.com/ec2/vmimport/
So there is no need to run VirtualBox under Amazon, one can just import and clone the VM as an instance.