Since you guys helped me find one of my teenage years white whale books, I wanna see if you can find the other one as well. This is a science fiction book. Plot is roughly:

• Starts with a nuclear bomb test. I think the protagonists are on an observation plane or helicopter. A UFO approaches, and protagonists black out.
• They awaken to find themselves on an alien world. The UFO that abducted them crash landed, and they set out to explore. There are two native peoples here, a very humanlike "good guy" one, and a hairy, ape-like "bag guy" one, who are locked in constant warfare.
• The protagonists side with the humanlike "good guy" aliens in the war, only to find out it's the hairy "bad guy" aliens who are the victims. They have to make the "moral choice" of either sticking with people who look like them, or siding with people who look alien but are "benevolent"
• I'm pretty sure one of the guys sides with each of the alien peoples. Hairy aliens win.
• The abductor aliens make themselves known. The UFO did not crash land, it was all a deliberate setup to test humanity's ethics. They return the surviving protagonist to Earth (I am not sure about this, could be they offer to let him stay).

The cover depicted a crashed saucer style UFO in a desert-ish alien landscape. Notable were binary stars overhead, that were trailing a spiral of material behind them. (I know covers mean little, since every edition gets a different one...)

Timeframe: Read the book in the mid to late 1980s, but the style and setup makes me think it was written in the late 50s/early 60s (of course I thought that about the other book as well so take that with a grain of salt).

Prior searched: A bunch of googling, unfortunately the main keywords from the plot are a dime a dozen. I also tried a google image search for the cover. No luck.

To be honest, I don't remember this book as being all that great a read, but somehow it stuck with me.