Rd.qubes.hide_all_usb.. how much protection?

When i installed my qubes i did so with the usb qube from the get go meaning this line was put into my grub configuration by default rd.qubes.hide_all_usb

I recently upgraded my sys usb to a disposable vm just because of the fact if the firmware of my usb devices infiltrated the qube then the infection would be lost on reboot. ( good security )

my only concern is that when i have been changing and upgrading vms would there have been any possibility off my usb devices coming into contact with dom0 ? even if rebooting ?

rd.qubes.hide_all_usb this line had been in grub file from the start which from what i understand makes the circumstance i have stated above impossible even if sys usb had been turned off., am i correct to assume this ?

please let me know . Many thanks