It would be sexual assault if Kirk assaulted Uhura. He didn't. They were compelled to kiss each other. Not all demonstrations of power and control fall under the rape heading. The point of this particular event was to force two people into a humiliating circumstance. They were not being sexually assaulted, they were being manipulated. Parmen committed no sexual assault. He made Kirk and Uhura kiss. He forced them into intimate contact, but Parmen himself did not commit any act of a sexual nature. The fantasy nature of their powers takes the rape and sexual assault out of it. There's no real definition for it because it couldn't happen in real life.
They were all abused, absolutely.
Here's Wikipedia's definition of sexual assault:
"Sexual assault is any involuntary sexual act in which a person is
threatened, coerced, or forced to engage against their will
, or any sexual touching of a person who has not consented"
Kirk and Uhura were both sexually assaulted. The definition of sexual assault does not explicitly state that it has to be between two people and that one has to be the aggressor, because there's no logical reason to limit it to that.
In most jurisdictions, it wouldn't be considered rape because there was no penetration. I think calling it rape would go a bit far given the context of the scene, but it's a valid argument to make.