There are few people at the clinic James actually respects. He openly antagonizes most of them, but there are two people he grows to tolerate.
The first is Hank, the van driver, who used to be an alcoholic. He is James's first friend in the unit, but we don't know why, exactly. Hank isn't more or less kind to James than others are at first, though he does let James borrow his coat. (James never returns it.) Hank also stands up for James after the toilet incident with Roy, and he helps James rescue Lilly at the end.
Coincidentally, James also tolerates Joanne, the staff psychologist, who is also Hank's fiancée. Joanne usually ends up being good cop to Ken's and Lincoln's bad cops, and although James always argues with her about AA, he's nice enough to never tell her off.
The rest of the clinic's staff isn't so lucky. Almost all the rest of them find themselves on the receiving end of Frey's Fury at some point. Many of them we see once and then never again.
Ken, the unit recovery counselor, loves to follow the rules, and he always tries to get James to follow the AA Twelve-Step program. His approach isn't that much different from Joanne's, but James hates Ken and likes Joanne, probably because Joanne is more willing to listen to James's side of the story.
Lincoln is the unit supervisor, so he's also a stickler for the rules. He finds himself in the enemy camp when he back up Roy, who's been blackmailing James after the toilet incident. (Lincoln, of course, apologizes when he finds out that James was telling the truth. Lincoln is the first of many people who end up apologizing to James over the course of the novel.)
Lincoln tries to stand up for certain people in the halls, like the Bald Man, who gets laughed at after telling his story of survival: "I didn't see any of you step up. You just sat there like scared little Boys" (2.2.275). But Lincoln kind of invalidates any honor he might have had by laughing when Lilly leaves; this prompts James to snap, "She's a Person, not a f***ing lesson" (3.4.721). James was probably just waiting for the perfect opportunity to put this guy in his place.
James also meets Randall, an attorney who doesn't work at the clinic but steps in to negotiate James's prison sentence, and Doctor Baker, the first named doctor we meet at the clinic. Baker puts James on two detox drugs (Librium and Diazepam), he stitches up James's cheek, and he, well, breaks James's nose. Hey, you have to hurt in order to heal, right?