I am using cream cheese frosting and wondering what to use for the crumb coat and does it have to dry before the cream cheese icing is applied?

A crumb coat is just a thinnish layer of icing/frosting applied to the cake to seal in the crumbs before applying the final coat. It is usually done in the same icing as the final coat. When I do a crumb coat I do allow it to "set" (in the fridge--I do not use a crusting buttercream) before adding the final coat.

Can you use a crusting buttercream for a crumb coat if you're using a crusting buttercream for your cake?

Yes you can use a crusting buttercream.