Over the years (decades now?) I have looked into hosting on Mac OS. The times that I have actually done so have allows been done in-house at clients site as part of an intranet.
I can tell you that your options are pretty few. http://www.macminicolo.net/ has been around for a while, but they specialize in the hosting of Mini's.
Another option is http://www.forest.net/ who has been around since nearly the dawn of the Internet, and who have always had Mac Servers as a specialty. Originally, they had a large number "Classic" Mac servers prior to OS X.
As I understand it, Apple allows VMWare to run OS X virtualized under Mac OS X server, but no other configurations. So your could talk to forest.net about running a dedicated Mac Pro tower running Mac OS X server and VMWare.
(Of course, you could try this on a Mini too, but I don't think a Mini will go far running multiple virtualized servers in production)