Oh, sorry…
Well, I don’t have the exact error message in front of me, but in short, /dev/serial… does not exist - file not found
Ok weird
Well, first we need to make sure the udev package is present on Ubuntu (the VM) because it manages that.
sudo apt update && sudo apt install udev -y
You restart the VM and you retest 
Bon…I did the update and installation of udev
By the way, it told me it was already installed
I restarted the VM anyway and went back to the Zwave integration
I still have the same list of tty but not (AMA0, S0…S30)
I try to select (a bit randomly) the AMA0 and validate
Messages:
Gladys is not connected to any Z-Wave USB key.
Attempting to connect to the Z-Wave USB key…
In short, no better than at the beginning
But why on this Ubuntu VM is the USB not recognized like on the other VM of the freebox? 
You don’t control the OS at all
In this case, go with a Debian VM instead of Ubuntu, I think you’ve understood but I don’t have a freebox to test 
Thanks!
It works on a Debian right away! We can see ACM0 in the zwave integration (in addition to AMA0)
And the USB Zwave stick is properly detected!
And my already associated devices are seen on the zwave network!
Note: I installed the usb-utils package before running the tests in Gladys (maybe this package should have been installed on Ubuntu too - to be tested)
It might be worth updating the tutorial in the documentation to mention Debian for USB management? 
( Installer Gladys Assistant sur une Freebox Delta | Gladys Assistant )
I made my first pull request 
https://github.com/GladysAssistant/v4-website/pull/12