I doubt that would work, at least not correctly and firmly. The FX1 apparently has holes(+threads) for bottom- or side- mount options, but you still need some kind of adapter/bracing/base -type stuff to go between it and the car. If you use the mfg's own brackets, it's a slider base that adapts between the 370Z floorpan and the side-mounts on the FX1.
You could start with any of the normal seat bases for our car (theirs, or Sparco's, or Planted, etc), and drill holes matching the bottom holes, but as you said you'd lose some angle adjustment unless you shim them. Shimming them safely will probably require more than a random set of washers, too - maybe make some wide shim plates of aluminum.
In any case: no, the "bottom mount" holes on a bottom-mount-able seat are not meant to bolt directly to the floor of the car. They won't be anywhere near the same place as the seat mount holes in our car, and both the seat and the car have threaded holes, neither has a bolt
. Something goes between the two. You could custom-fab that something to minimize height, but it might be easier to use one of the bases listed above as a starting point and just modify it.