sound hole to reciever

It can.  I don't know if it will on all stereos, but I remember doing that way, way, WAY back when I got my first pickup (a passive Schaller) for my first acoustic.  I had a Realistic boom box (made by JVC I believe for Radio Shack) that had an AUX input.  Had to use an adapter if I recall, but it worked.  Didn't work great, but it worked.

I have no idea if that would work on modern stereos, but it can't hurt to try.............at least I don't think it can hurt to try.    

aux input is 1Vp-p
depend if pick up puts out a 1v signal or a microvolt signal and requires a preamp
you will find out quickly

Huh.  I wonder.  If it's got a mic input, I'd assume it uses the 1/4" jack?

If so, I wonder if you just plugged the patch chord from an acoustic into that, would it work?

I'd try it just to satisfy my curiosity!  lol.

The passive pick-ups I have used needed some kind of a pre-amp to get a usable signal.

I have a very small, cheap acoustic amp. It is an old Epiphone practice amp bought used.
And I have a passive sound hole pick-up, (cheap), I run the pick-up into the small amp and run the output on the back of the amp to our PA system.

Without the little amp the PA doesn't have enough signal to work with, you can't get enough volume out of it. I'm afraid your AUX input would need similar.

I would try it, if you are "back porch picking" you might be fine with it.

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