Here's another thread on it: http://www.linda-goodman.com/ubb/Forum10/HTML/002472.html It's an interesting idea the planet of boundaries being in the house of no boundaries.
Maybe the Saturn person will feel the sense of nebulousness of the other person's 12H and get a secondhand impression of wistful other worldliness and have their fears triggered because it will strip the Saturn of it's boundaries.
What the SATURN (edit) person does with this depends on the rest of their chart and the aspects to that Saturn. And also how that Saturn person relates to Pisces/12H energy - whether or not they can relate to it in some way, feel endeared by it, and therefore will be able to accommodate and manage it.
The Saturn person if fearful though being in that boundless space, may project onto the house person. The house person may be viewed as in some way boundless, undisciplined, lost at sea, wishy washy, directionless, useless, deceitful or evasive etc. And then, being Saturn may fearfully deride, lash (if Mars gets activated) or criticise the house person.
I don't imagine Saturn would be great in this house.
Will the house person feel low level like they can't relax? Or will they feel low level supported and guided? I'm not sure. The 12H IS a sextile to 10H (Saturn ruled house). And Caps are pretty protective with Pisces. And Saturn does like to parent. So, maybe either way, depending on the aspects?
Or maybe it starts this way until the boundless energy of the 12H kicks in and then the fears with it.
Just my random ponderings on it.