Smoke is not just a gas.
What is smoke?
Smoke is a collection of airborne solid and liquid particulates and
gases... - wikipedia
Before this question can be answered we need to know more about both devil fruit abilities. Like what kind of gas(es) can Caesar (originally) transform into.
As stated by Caesar himself, he altered his own Devil Fruit with his
chemical expertise, adding many of its offensive abilities, thus, the
original abilities of the Gasu Gasu no Mi remain uncertain -One Piece Wikia
Unfortunately we don't know enough for example about the types of smoke and gases they can use to really answer the question.
They both can also make there element have a high density to do things like grabbing objects.