I confirmed that vmware 5.5 is compatible for CUCM 9.1 and also that it will run on my Dell Power edge 1430 server. Challenge now is how to actually install the ESX as the CDROM in this server is not working.
With some quick searching however I found these two articles which turned out to be very helpful. I actually got it working with the first method but was interested in a code approach so I did it again just for the fun of it and also to prove the second procedure.
In comparison however I must say the code approach was much cleaner and faster so will use that method for future needs to make USB drives bootable from a macbook.