[Taqwus]

Regarding Miasma, I suppose it depends on what sort of diseases are involved. Plant men may not be subject to malaria, but perhaps there are plant ailments. Perhaps anything with 'swamp survival' should be immune or highly resistant as well.
On diseases in general, I recall that some units -- undead in particular -- can get the disease flag while not suffering its effects. I suppose it might matter /if/ the unit is polymorphed, picks up a Lycantropos amulet, or casts Transformation if the flag is retained. On some undead, this makes a degree of sense -- a walking corpse might be inhabited by pathogens, although some won't affect it too much (but other infections would -- sarcophages) -- but perhaps ethereal units should not (?). It's all academic if the disease flag is lost on transformation, however, and the disease is non-contagious as most are except for leprosy auras and certain death items IIRC.
Golem Cult might be an interesting pick with Ulmpunk, but that mod might have #nothemes, heh.