Good point on making it a tough issue. That does fit better with the text generally. However, I find it hard to say that the Inchoroi are good, or at least amoral, when they specifically manufactured bioweapons to desire nothing but rape and inflicting pain on humans/nonmen. Sounds, to me, like saying Hitler was a hedonist, he just wanted everyone to be happy, but his natzi's were the evil ones. This situation is more ambiguous, and indeed we know more about hitler than the Inchoroi, but it demonstrates the general idea.
On the other hand, lets try and look at it from the pro-hedonist POV. The Inchoroi manufactured a race of biomachines to erratic life on a planet. The sranc, who's only objective is an evil one, endlessly enjoy the task. It gives them extraordinary pleasure. Seems like a nice thing to do, or rather, the nicest thing they could do given the situation.
I still don't really buy it though. The Inchoroi have spent an enormous amount of time warmongering, exterminating planet after planet, and generally trying to kill things, for me to call them purely hedonistic. I could certainly believe that they were that way, but after the IF and learning of their damnation, they self admittedly don't give a shit about anything else but their own salvation. Exterminating the universe for your own pleasure and safety, seems a whole lot more sadist than hedonist.
They could make anything via the Tekne. Why not eradicate the men/nonmen by making loveable alien critters, nigh irresistible, so much so that all lifeforms on the planet forgets to procreate and instead just endlessly has sex with your robots? Or promise, and provide, everyone with endless neuropuncher pleasures, narcotics, food and shelter, all within the safe confines of the Arc. Everyone lives in harmony. Now, that is hedonism. Construct a race a sadistic biomachines to rape and kill everyone, that is sadistic.
From what I can discern, the Inchoroi are sadists. Do they enjoy having a good time? Sure. But their damnation changed them, irreparably.
A different question may be, do the Inchoroi know and or recognize that they are sadistic, or are they unawares of the perception of that nature and thing of themselves as purely hedonistic? Again, though, I find it hard to believe that they would think the latter. However, self delusion is an extraordinary thing, and I think their answer, reguardless, is largely irrelevant to the discussion.