I've spent a total of 38 hours trying to get Xen VMs into VMware and for 24 of those, have been completely unsuccessful after trying countless methods found here and on the Googles.
I've migrated a 2008 R2 PVS image, multiple 2008 R2 application server images, and a 2012 R2 Citrix License server all successfully with this method.
This method involves using Veeam Backup and Replication, but you should be able to do a straight export from Xen so you get the VHD into a readable file.
The method I've found that finally works is to be the following:
1. Backup your Xen VM using Veeam Endpoint Backup (if you choose to use Veeam, you can restore the Endpoint Backup as a VHD to a local drive to convert it in the next step, this is 10 times faster for me) or use your own method to get the OS VHD onto a Windows box (export OVF to Windows storage)
2. Using Starwind V2V Image Converter, choose a local file (your newly exported/backed up VHD) and export to a Growable Size VMDK, MAKE SURE you choose IDE and not SCSI (the whole point of this conversion is to get the VHD to use IDE)
3. Import the newly converted IDE VMDK into a datastore and create a blank virtual machine, Ver. 11, attach the newly import VMDK, SCSI controller does not matter as it will not be used since we're attaching an IDE VMDK, do not include a NIC at all at the moment
4. Once your machine is created and imported VMDK attached, snapshot the machine before powering it on, you will need to boot directly into safe mode by spamming F8 in the console. If you get a blue screen you will need to revert to snapshot (this took me 25 tries on my first VM, only 1 try on the rest) enabling first boot to bios before turning the machine on made this much easier for me, I exited the bios and spammed F8 and would always get the Safe Mode prompt
5. Choose normal Safe Mode and get into the OS with the local administrator account. Once here, open CMD prompt and enter REG ADD "HKLM\SYSTEM\CurrentControlSet\Control\SafeBoot\Minimal\MSIServer" /VE /T REG_SZ /F /D "Service"
6. You can now open Add/Remove Programs and uninstall "Citrix XenServer Windows Management Agent" (My PVS image actually didn't show XenServer tools installed, but the files were in C:\Program Files\Citrix\, if this happens, mount the XenTools ISO in VMware and reinstall them, then immediately uninstall and continue down the list)
7. Once XenServer Tools are uninstalled, do not reboot, first go to "C:\Windows\System32\Drivers\" and delete Xen.sys
8. You should be good to reboot normally now, once you're back into the OS in normal mode you can add a VMXNET3 NIC and a CD/DVD drive and install VMware tools
9. You're done, you're VM has been successfully migrated to XenServer
Obviously your results may vary but after trying at least 35 other methods this one is the only one that worked. So far I've had no issues with the converted VMs and they have been backed up in VMware via Veeam B&R with no issues.