We never saw anyone in the detention block except Leia, and no dialogue supports anyone being there besides her. And why would there be? The Death Star is brand new. They hadn't DONE anything yet except fly to Alderaan and blow it up.
On the other hand, when Luke and Han brought in Chewie under the pretense of a "prisoner transfer from block 1138," the detention-center guards didn't seem overly suspicious of the assertion that they already had a Wookiee prisoner in custody. You'd think if the detention center were empty aside from Leia (and maybe the rest of the survivors of the Rebel Blockade Runner), the guards would've already known they had no Wookiee prisoners and would've instantly caught on that it was a trick. It implies that the detention center must've been very full if the guards could believe they'd overlooked a Wookiee.
Of course, the real explanation is that Lucas was just making a bit of Saturday-matinee fun and never expected anyone to put a lot of thought into deconstructing its plot holes, let alone its ethics holes.
So yeah, Luke is directly responsible for the deaths of thousands upon thousands of people. But they were, like, BAD and stuff. So it's okay! They had it coming!
Oh, yeah, I'm sure they only hired evil janitors and plumbers and IT techs. All the Empire's job sourcing was done on the planet Henchmantooine.