pool filter sand on top of dirt should be fine. Just watch out for "compacting". I'm using play sand, which is a bit finer IIRC. You'll want to poke the sand every now and then, and be careful not to poke to far.
In my 55G all the pots were topped with sand or old substrate. It's my "test" tank to figure out how plants grow/etc so I could come up with a good aquascape for the 125G.
What I'd recommend (from experience) is to put the soil in water. All the peat + woody items will float to the top. scoop that out and keep what sinks. I experimented with keeping this stuff in vs. sifting it out. I had a few pots where the sand cover "exploded" when submersed. Nothing worse than cleaning up the tank, but luckily the pots were removable. Can't imaging if this was my main tank! Oh, also remember that if the soil has peat, and the peat gets into the water column then it *will* stain the water (which can be attractive). The sand cap should help prevent this.
Also, you may want to put the sand in a pillowcase and spray it with a hose. This should get rid of any fine sand.
Here's my 55G with pots
For the 125G, it's really not ready for a journal. I'm still futzing with it, but I promise I have pictures for when it's matured in 6 months.
Finally, you should check out the "Fraternity of Dirt" group here. Everyone in that group is using dirt substrates capped with something. I'm sure one of them is using PFS rather than play sand, so they might know better if there are any gotchas with PFS.