I'm building a XenApp 7.5 (Same code as XenDesktop 7.5 only a different license) environment, and hitting a wall when creating Machine Catalogs. Under the step "import or add virtual machines", I click on the "Add VMs" button, and can't browse past the top level of my vCenter cluster and can't see any vm's. I checked http://support.citrix.com/proddocs/topic/xenapp-xendesktop-75/cds-vmware-rho.html and the account I'm using meets the permissions requirements. I know that the issue isn't with this XenApp DC because I am able to connect to our secondary data center and browse vm's from this same DC.
I opened a support ticket with Citrix and VMware and after two weeks it still wasn't working.
While I was looking at the differences between the working and non working data centers, I noticed that in the data center that's working, I can only see vm's that are not part of a vApp in the Citrix Studio Console. I moved my XenApp 7.5 vm's out of the vApp and I can now connect to them with Citrix Studio.
If you are connecting XenApp or XenDesktop 7.5 to VMware vCenter 5.5, don't place your Citrix virtual machines to be managed inside of a vApp. I can't verify this issue on other versions of Citrix XenDesktop/XenApp or VMware vCenter.