Hello,
Of course, you can run Kentico CMS in a cloud environment. Our clients already use Kentico CMS in 
Windows Azure, Amazon EC2 and Rackspace Cloud.
We also offer 
Kentico+ which is Kentico EMS running as a service in the Windows Azure cloud for a monthly fee.
Or you can try to contact one of 
Kentico Hosting Partners, e.g.: 
NetConstruct who are already building their solutions on the RackSpace.
And for sure, you can have everything installed just on one server.
Best regards,
Martin Danko