You said, and I quote:

"Hardy biology might well adapt and thrive under the circumstances. Examples on Earth of acid loving microbes aren't common, but they exist, and there's no reason to think they couldn't exist and thrive on Mars. Part of the key is to set to the side the premise that biology on Mars would arise and evolve under purely watery conditions and think instead of how (and whether) Martian biology could develop under the highly salty/acidic conditions that may have been more prevalent and might still prevail beneath the surface."

A very important point regarding the possibilities of any native Mars life.

The big question is, has anyone done the research on this?

If Mars was friendlier to life in its early days, we might still find it in
fossil form at least. Assuming NASA or some other agency will ever
seriously look into this. Not to sound Richard Hoaglandish here, but
there were some odd-looking objects in a number of MER images which
I and others felt required more serious investigation. Instead we got
the fringe element doing all the "investigating" and making sure that the
subject is left unapproachable by mainstream science out of fear of
being discredited.

At this point it will probably take a manned expedition to look for and
uncover any Martian fossils, as while NASA pays lip service about
searching for alien life there and elsewhere, it remains much too
cautious on the subject.

And we won't be landing on Europa, Enceladus, or Titan any time soon,
so it will probably be our children who get to find out if there is or were
any other life in the Sol system.