Why do you think it would be? If 200 humans share enough air to dilute the relative concentration of poison in that air effectively, none of those humans will receive lethal doses of poison.

Only if the concentration reduces over time and the oil isn't enough to poison everyone in 69 seconds anyway.

The people can keep filtering a certain volume of oiled air, but at some point it's too much oil in their body.

I'm certainly worried about the health of those people in the bigger part of the airplane.

If the people in the cockpit are incapacitated, though, it's a problem for everyone on the plane. The oil has nasty stuff that kills the pilots, but it's also hard to see through.

Basically, at the very very least, let's not dump the oil into the cockpit. Ideally let's not dump the oil into the passenger compartment either, but sheesh, let's not kill or blind the pilots as table stakes..