I am running a Raspberry Pi 4 with HAOS. I am trying to configure the UDEV rules and are unable to find UDEV directory. I am using the SSH add-on and I suspect the UDEV is not available when using the SSH add-on.
How do I SSH into HAOS directly?
I doubt it’s related to using the add-on.
It’s more likely that it’s not available just because you are using HAOS which is a pared-down version of a normal OS and a lot of functionalities have been removed so as to not “confuse” 
less tech savvy users.
I don’t use it so I may be wrong tho.
I don’t use hassos either but it looks like you can load udev rules in by booting from a USB somehow based on the instructions here
If you are running HAOS, you are running a container environment. So typically, you should not need access to core OS functions. Is there something out of the ordinary that you are trying to access in the HA application? Even after adding in some additional HW, it might not be passed through to the HA container.
I like to create persistent device names for my Nortek HUSBZB-1 Z-Wave and Zigbee controller.
While I don’t use that device, typically it is only a problem when people unplug and re-plug in the device while HA is running. I have a USB Z-Wave stick I have had since I started using HA and not seen a requirement to lock in the udev rules.
Having said that, I thought I read something in either the recent or upcoming release notes about a wizard to configure new USB devices. Maybe that will address your needs.
The default ttyUSB0 and ttyUSB1 work well in the integrations, but it seems cleaner to have the devices called ZWave and Zigbee.