No. It's theft, invasion of privacy, piracy maybe (The infringement type), but not rape. Rape denotes a damage being done, an assault.
And there is hardly any damage done from the Inner Light's dream on Picard. He wakes up and has experienced a very long, pleasant dream and gained a ton of knowledge.
And people who suffer from physical rape still may get orgasm, or at the very least get to have sex, and in some cases gain the gift of life within them. All of that aside, there can hardly be any "damage" from rape itself other than strong emotional damage. There doesn't always have to be a physical violence other than the deed itself. Hitting, knives and the like.
And you could argue Picard *did* suffer a good deal of emotional damage having lost a lifetime's worth of friends, loved ones, children and grandchildren.
The point is that Picard was an unwilling participant in this. He was knocked out and had decades worth of memories forced into his mind. That at the end he came out of the experience having had a positive experience is irrelevant to the idea he still had the entire experienced forced on him.
And, realistically, there'd be some lasting damage and we get a slight hint of this later in "Lessons" when Picard shares his flute-playing with Darren. He still has to deal with the loss of a family. Yeah, a family that never existed but from his point of view they did. The memories he has are as strong and as vivid as any other memory in his head.
Hell, if we really wanted to we could argue that those 40 years worth of memories could damage him some manner in that it's taking up "more space" in his brain. I'm not sure what the neurology of it all says but I suspect the brain doesn't have an infinite capacity to hold memories. So what do these extra memories mean for him? Is there going to be a point where he can't form new memories as he continues to age? Are his oldest memories going to go away to make room for the new one?
How well can he remember his earliest memories? From his perspective they're decades further into the past. He's a man in his 60s who now effectively has around 100 years worth of memories in his head and by 24th century standards he's middle aged!
Seems like there could be a good "deal" of harm here. That he came out of the experience having enjoyed it, remembers it fondly and arguably a better man. Is irrelevant. The entire experience was still
forced on him! He was made to experience something against his will.
This isn't the case where we think of Troi or Lwaxanna who simply can "read" minds or maybe talk through the mind, in neither case are the actively invading a mind and forcing their will and own ideas/thoughts on someone.
How is it possible to not see this anything other than a clear violation of Picard's body? Memories, 40 years worth, were shoved into his mind against his will. That's a pretty damn severe violation.