On a host running XCP-ng 7.6 I tested the tools on 2 VMs:

1. On new install of Server 2016: Ran XCP-ng tools' setup.exe as administrator which gave a "Windows Management Agent failed to install" error message. Then remembered I needed .net framework 3.5 and installed it then tried again. Installed successfully and was prompted to reboot. It appears to be working correctly. Both XO and XCP Center tell me the management agent is not installed on the VM (though I believe it is). You might consider adding a reminder about the .net 3.5 requirement in the setup.exe prompts.

2. On existing install of Server 2016 with .net 3.5 installed: Uninstalled Citrix guest tools then rebooted. Server came back up with full capabilities of guest tools and correctly recognized NIC. From what I can tell, Citrix's tools didn't actually uninstall. I then installed Citrix's guest-tool-leftovers uninstaller (xluninstallerfix.exe), ran it, and rebooted to a blue screen. Restored to snapshot. Attempted same process (xluninstallerfix.exe) then installed XCP-ng guest tools before reboot but still blue screen. Attempted to remove Citrix's guest tools in safe mode using the process described here: https://antisp.in/recovering-windows-server-2012-on-xen-server/ (author fails to mention you need to manually start the two services). Restarted several times but Citrix's tools are still active. Did the same thing with xluninstallfix.exe in safe mode and then attempted to install XCP tools while still in safe mode. XCP tools failed to install as it was unable to start a service (error 1603, related to task scheduler I believe). After several failed install attempts rebooted to another blue screen. I could have booted to safe mode again but I'd still be unable to install tools in safe mode so out of luck.

As far as I can tell it works great on new VMs but there seems to be no way to safely replace Citrix tools with XCP-ng tools at the moment.