Is it possible to use the Whonix host hardening packages like lkrg, on Qubes Debian templates?
I am not sure host packages still makes sense to offer this under the Whonix umbrella. That is because now Kicksecure is available under its own domain name.
Related wiki pages for host packages:
But those are community support only.
It might be better to forget thinking about host hardening packages. If Debian host hardening or Qubes Debian templates hardening is desired, you could look into Kicksecure instead.
(Whonix is based on Kicksecure.)