I'm also trying to run it on nixos. I wrote all of the progress/details so far here: https://github.com/NixOS/nixpkgs/issues/64344
libsvpflow works, SVP Manager - same problem, "This option is not available. Please see --help for all possible usages". It comes from the 'zenity' - SVP Manager still fails even if it's not present through. I have no clue why.
As for error 255, it's about missing ocl-icd package - and it needs to be specified in hardware.opengl.extraPackages list. That should put libOpenCL into /run/opengl-driver/lib.
Then libsvpflow needs to have that in it's rpath. In the linked github comment I've included "svpflow.nix" derivation: it only installs the libs without SVP Manager (which doesn't work), and they're available under /run/current-system/sw/lib/libsvpflow1_vs64.so (and the same for 2).