I'm certain it was published before 1998, fairly sure before 1994, in paperback.
The background setting of the novel was the distant future, when humanity was part of an interstellar, possibly galactic, federation of civilizations. The legal system of the federation barred corporations from plundering the resources of a planet if there were any signs of intelligent life on it. Should a species of intelligent life be suspected, a special task force would be dispatched to determine if the species was, or was not, sapient.
The local setting of the novel was a planet that had been identified by a corporation for its profit, but a human-like species was found to be living on it. The planet had a strange ecosystem: the humanoids wandered disparate regions in isolation, keeping a fairly precise distance between them all. The local trees would grow fruit for the humanoids to eat whenever one was hungry. When accidental deaths occurred, two of the humanoids would come together to procreate and replace the missing person.
The protagonist of the novel was a team leader tasked with assessing whether or not the local species was sentient. He knew the legal system was rigged in favor of denying sentience, and that this local instance was going to be easier to deny than others because the humanoid aliens were so different from humans in fundamental ways. (A humanoid presented to another team member induced emotional distress, not unlike the Uncanny Valley experience.)
The plot of the novel involved the team leader pulling together a unique team. Ostensibly, they would be assessing the humanoids for sentience. In reality, they would be faking sentience: a language expert would create a brand new sign language, and the team would teach it to their captured humanoid alien. They would make the humanoid dress and adopt mannerisms that would be recognized for signs of sentience.
One of the team members was forced on the team leader: another alien from an empathic race. They didn't speak, but could produce emotions in people and even control behavior to a significant degree. The team leader had no idea what the empath's purpose was.
Another team member was a specialized soldier. This soldier used self-hypnosis techniques that would turn off his conscious mind and propel his body through combat maneuvers, referred to as "dances." Some of these dances were complex enough for a single soldier to disable an entire battleship. (There was a snippet of the story where the soldier and a woman on the team have sex, and she regrets that it was "just another dance.")
At one point in the novel, the soldier attacks the empath with a homicidal dance. The empath uses their mental powers to compel the other team members to block the attacks with their own bodies.
At another point, the humanoid alien has been taught enough, and his behavior has been changed enough, that he can no longer make the local trees supply him with fresh fruit. In the midst of a massive thunderstorm, the humanoid alien dies outside, constantly giving the learned sign language for "No!"
