I have a "parent" model with two nested submodels. Submodel A creates a gdb & FC's. These FC's are output and exposed as model parameters to the input of Submodel B which exports them to CAD. When I validate the parent model, submodel B does not validate. I'm guessing this is because its input has not yet been created from Submodel A? When I run the parent model, I get error 000732 that the input features do not exist. I'm guessing this error is caused by the same reason. How do I get around this error?
You are on the right track. You can set preconditions in Arc Model Builder to control the order in which parts of the model run. You can either set them by right-clicking the tool and selecting Precondition from the pop-up menu or by using the connect tool (see here). You can also use Booleans and Positive integers to act as preconditions (possibly set by some other event).