Also it's worth pointing out that Mr. Gray wasn't a throw-away, 5 minute character, he was the key to a successful resolution of the plot. The whole final confrontation hinged on him being a fundamentally good person, and willing to do the right thing (i.e. stand up the military and Psi Corp (and in fact Mr. Bester specifically, since it was hinted that that whole episode was payback against Sinclair)). And the fact is he wasn't a commercial teep, he was a military assistant. So the fact that he was trusted with this assignment (a revenge, trumped up attack on Sinclair) and the fact that he STILL proved to be fundamentally good says to me that there have to be a lot of Psi Corp teeps who are just normal, good folks. If he was a fluke then he wouldn't have been trusted to be there in the first place, they would have picked someone far more reliable. To me, that's an example that proves that there have to be more like him, and a lot more, or he wouldn't have been there at all. He's a solid character with a backstory, personality and motivations, so I think he's a perfectly valid counterexample. And if he's a valid counterexample I think you must reexamine your assumptions.
Add to him Byron (who WAS loyal Corp when he decided killing was wrong, not to mention under Bester's direct control/brainwashing and he still broke free), the one from Crusade whose name I can't remember (who was also corp loyal until he realized the corp was bad and acted against it), Lyta (who was corp raised until she decided to make a run for it), etc etc. It's worth bearing in mind that most rogues aren't just on the run from the start. Most of them are in the Corp and THEN run which says that they clearly don't agree with the Corp for some reason. You can't discount rogues, since every rogue from the Corp was at one point simply in the Corp but unsure about whether to run. Every rogue from the Corp had doubts, experiences and problems that eventually led them to run, so playing a nice, doubtful Corp character is perfectly legitimate. You could even play a loyalist who had compassion and still wanted the Corp to come out on top, thinking that while it's bad, it's better than nothing.
I think the key here is not that all Psi Corp telepaths are evil, manipulative and murderous but that every Psi Corp telepath has seen the real face of the Psi Corp. The common thread in every single teep story we have is that the Corp has to reveal itself eventually. Lyta's experience interning with the Psi Cops, Talia's discussions with the telepath underground railroad, Byron's order to fire on civilians, Ironheart's experimentation, Mr. Gray's involvement in the Eyes affair, Crusade's teep's meeting with the rogue...and on the other side, the Bloodhound units hunting their own, Bester's various problems from the books, Black Omega attacking civilians, the Psi Cop working with Morden and EarthDome, etc etc. The difference between the loyalists and the rogues are that the rogues reject what they see, while the loyalists do not (whether out of simple loyalty, brainwashing, or because they know that while the Corp is bad, it's better than the alternatives).
So, to summarize, a telepath like you describe is perfectly legitimate. However to select one outlook as the only valid one is wrong, and does a disservice to the variety and depth of telepath characters we have seen in the series.