Note that in the case of an ascetic, they can still be targeted by abilities in a backup state, as their role does nothing. The key difference in the case of the doctor is that "investigate as having no gun" is
not
a passive property of the doctor.
It's a passive property of the gunsmith
, that they investigate doctors as having no gun. The backup role doing nothing does nothing to affect the gunsmith's result, because even though a backup doctor does nothing, it
is
a doctor with a modifier on it, and in normal games gunsmiths get no gun results on doctors.
A quick look at the Gunsmith role tells me that my interpretation is correct:
Normal Guidelines
In Normal games on mafiascum.net, a Gunsmith gets guilties on all Mafia (except Traitors and Doctors), Cops, Vigilantes, Gunsmiths, Role Cops, Vanilla Cops,
Backups of roles with guns
and JoATs that have any of these listed powers.