Engine brake? I'm not thinking so... White smoke typically indicates it's burning coolant, and black is usually engine oil. Gray is usually unspent fuel, and you may see a little of that if you have an exhaust brake, but not the others.
What year IC, and what engine? Do you know any of the mechanics who can put ServiceMax on the truck (just takes a few minutes to run for DTCs)? We have some '06 ICs with DT466, and have had two EGRs develop holes in the coolant core. Lost a turbo on one of them, since the additives in Shell ELC solidly gummed up the wastegate.
To protect yourself, make sure you continue documenting the issue on your DVIRs, and ensure you have copies of all of them. Document all discussions with your manager, and everyone else as well. Engine performance is not a vehicle safety issue for the cops or DoT to involve themselves in, so you're safe there. I can't speak for emissions, but I'd think your bundle of DVIRs with smoke written up would help you on that, with any reasonable officer.