So, Christopher, it is entirely possible that the Hur’q, which is not this species actual name but the Klingon designation for them, are indeed one and the same with the Karsid?
I doubt you could reconcile
Ishmael's idiosyncratic, crossover-laden version of the Trek universe with the one established in later canon. Sure, you could amuse yourself with the pretense that the Hur'q backstory was pretty close to the Karsid backstory from the novel, but there are bound to be details that conflict.
It is possible that the DS9 writers copied or were somewhat inspired by this storyline from the book Ishmael and used the Karsid/Hur’q subjugation of the pre warp Klingon homeworld as a basis for the background of the episode The Sword of Kahless.
Of course they didn't. Laypeople always want to assume that any remote similarity they see between two stories is "proof" that one copied the other, but that's naive. The fact is that writers tell similar stories by accident all the time, because there are only so many meaningful ways to put concepts together, especially when working within the same universe. As a rule, we try to
avoid copying stories that others have already told, because nobody wants to be accused of being imitative, and because the people who buy and pay for works of fiction generally want them to be original and fresh. One of the main reasons that stories get rejected is "Sorry, we're already doing one like that." It's annoyingly difficult to avoid copying someone else's idea by accident. So if a writer does find out that someone else has already done something, we'll usually try to do something different.
That means that you have it backward to assume that a similarity is proof of copying. Usually, the fact that two ideas are similar to each other is proof that the later writers did
not know of the earlier idea. If they had, they would've changed their story to be more distinct from it.
If the producers had directly referenced or copied story points from Star Trek books then they would probably need to pay the writers royalties for the use of their ideas or characters.
No, they wouldn't. That only applies to people who write for the TV shows or movies. Tie-in writing like novels and comics is work-for-hire. Everything we write in the
Star Trek universe is the property of
Star Trek's owners. If they want to, they're perfectly free to use any concepts from our tie-in fiction, because we write it on their behalf as their hired contractors. It's just that they usually don't, because they're too busy making their own shows and movies to pay much attention to what the tie-in books are doing. They have plenty of ideas of their own to keep them busy, and approving the tie-in books is generally left to the folks in the licensing department to handle.
Why would Starfleet covering up the location of the Klingon homeworld by simply referring to the homeworld as the Klingon Homeworld during TNG be a conspiracy?
A cover-up requires multiple people working together to conceal something, which is the definition of a conspiracy. But the point is not about the definition of a conspiracy. It's that conspiracy theories are driven by an irrational need to postulate an imaginary, overcomplicated, bad explanation for something when there's already a perfectly simple and innocuous explanation. The simple, logical explanation is that the initial projections of the need to evacuate the homeworld were wrong. Either they discovered things weren't that bad after all, or they found a scientific solution that let them save the homeworld's ecosystem. First impressions are often wrong. There's nothing unlikely or unusual about that. So there's no reason to assume the homeworld
had to be evacuated, and thus no reason to invent an overcomplicated cover-up theory.
The destruction of Praxis could also have been detected by Dominion scouts who had come through the Bajoran wormhole long before the Dominion fleet did and had been gathering intel on the species of the new territory using Shape Shifters.
That's also the same kind of mentality as conspiracy theories -- manufacturing hypotheticals with no basis in evidence and going off in complicated spirals with no connection to reality.