Enforcer involvement isn't the issue. Hibiki understands that he, Gale, and Stephan will need Enforcer backup to take down a mass Rocket gathering, as they themselves probably won't be enough. The issue is that Stephan is asking Hibiki to abandon his moral principles and deceive Beige into a trap.
Stephan: Just you, alone, could go into those sewers after Beige and trick him somehow.
Stephan: Now, we just need to place him with Hibiki and it'll look like Hibiki's been invited to join Team Rocket. But he hasn't!
Stephan: We'll be waiting here. Just lure him out, that's the plan.
See what I mean? Basically, Hibiki's alignment is Neutral Good, which means he believes in defeating evil in an honorable, no-luring, no-trickery, no-guile, no-deceit way. Perhaps Stephan is of the mindset that "the ends justify the means," which is why he can't understand Hibiki's continual hesitation, but . . . in your post, Stephan's gonna have to make up his mind whether to play things straight with Hibiki, do the operation without his help, or try arresting him for defying orders. Hibiki's drawn a line in the sand, and he ain't crossin' it.
