It's a PC DOS port. But honestly, where are the NTSC Amiga versions? Never seen one. And the PC DOS screens looks a bit squished too. Of course they are US developer. But i think the Amiga game version was developed on PAL Amigas from a european team.
http://www.mobygames.com/game/dark-seed/screenshots
edit: The manual lists a Cyberdreams UK Ltd too.