In the opening chapter of the book, Hal is the narrator and his narration is eloquent:
I am seated in an office, surrounded by heads and bodies. My posture is consciously congruent to the shape of my hard chair. This is a cold room in university Administration, wood-walled, Remington-hung, double-windowed against the November heat, insulated from Administrative sounds by the reception area outside, at which Uncle Charles, Mr. deLint and I were lately received.
I am in here.
Three faces have resolved into place above summer-weight sportscoats and half-Windsors across a polished pine conference table shiny with the spidered light of an Arizona afternoon. These are three deans - of Admissions, Academic Affairs, Athletic Affairs. I do not know which face belongs to whom.
I believe I appear neutral, maybe even pleasant, though I've been coached to err on the side of neutrality and not attempt what would feel to me like a pleasant expression or smile.
...
"... wood-walled, Remington-hung, double-windowed ...
"I am in here."
He's very aware of what is going on and of his state. But, what you say about his tennis is interesting. Hal's life is dedicated to playing tennis, and he competes against the same people that he socializes with. After completion of the day's competiton, Hal sneaks off into a sub-basement and smokes pot in total isolation. Then, he re-emerges to socialize with his competitors. I agree, smoking pot is not a type of rebellion in Hal. Hal's life is fractured into disconnected bits. Smoking pot helps him to hold things together.
As you say, Hal was trying to stop using drugs. Maybe he did and that leads to his fracturing.
During Hal's interview, they bring up a list of his essays,
Neoclassical Assumptions in Contemporary Prescriptive Grammar, The Implications of Post-Fourier Transformations for a Holographically Mimetic Cinema, ..., A Man Who Began to Suspect He Was Made of Glass, Tertiary Symbolism in Justinian Erotica. These sound like scholarly essays, like Hal is a serious thinker. Out of all the essay titles, the one that stands out as different to me is
A Man Who Began to Suspect He Was Made of Glass. Hal? Did Hal stop smoking pot and break into pieces?
I'm also thinking that a big connection between Hal and Gately is Joelle. Orin's girlfriend, JOI's star, Gately's helper. Either I don't remember, or didn't get the part about JOI's ghost visiting Gately. I'll watch for that in my reading.