LTC3588-1 circuit model LTSpice export
Models in LTspice have, in general, a SPICE-compatible format. If you find a model in LTspice, open it up with a text-viewer (not Notepad, one that handles Unix endlines), and check the syntax. If it doesn't have LTspice specific elements, such as A-devices, for example, then you should be good to go. The only thing that remains to check is whether if it actually works in SIMETRIX.

If, OTOH, the file is encrypted -- which happens to be the case here -- you're out of luck, since encryption only works for the software that generated them. You can check if it's encrypted by looking in My Documents/LTspiceXVII/lib/sub/LTC3588-1.sub. The extensions do not matter (at least in LTspice they don't), since the .inc or .lib command accepts full paths. I don't have SIMETRIX but I don't think they work any differently (if I'm wrong, let me know).