Is this recipe crusting or noncrusting:My Easy Chocolate Buttercream Frosting? I plan on putting it under chocolate fondant and want to make sure it is the right kind. Does it need to be noncrusting under for the buttercream and crumb coat layers?

You can use either non or crusting b'cream for cumb coating.
What makes it crust is a higher amount of sugar to fat..... so if your recipe has 1 cup or more of Crisco for each pound of powderd sugar it will take longer to crust; if it ever does.

But does it matter under fondant which buttercream I use?

It doesn't matter, I have used both. What matters is that the buttercream is as smooth as possible so the fondant doesn't show any lumps or bulges.