Yes... no Vaseline or any other products on your bird's combs will prevent frostbite. I don't know if it can help cause frostbite or not, but I do know it doesn't help anything. The only real solution is to give them heat and keep them inside if it's windy. Everybody here in Alaska just gets used to the fact that the little tips on the combs do indeed get frostbite and turn gray, sometimes a speck of black. They don't seem to notice, and it doesn't seem to hurt them. The combs just heal up when warmer weather comes (although sometimes a tad grayish on the tips still) and it's onward and forward. Just as a point of reference, my birds have been in weather as cold as 20 below (overnight) without harm when things got colder than expected. When it gets below zero, I plug in their red 250W head lamp on a timer and it runs a 50% duty cycle, 2 hours on, 2 hours off, all day and night until the weather warms up. As soon as it starts staying above zero again, I unplug the heater. Chickens are pretty hardy when it comes to the cold.
Brian