In response to your question, I have good news and bad news. The bad news is that he can absolutely bring up case law and common law at the hearing in support of his argument.
Now for the good news. Unless the case law specifically overrides the statute, the statute is typically controlling. Then, case law is decided in this order from least persuasive, to most persuasive. Superior court, Court of Appeal, California Supreme Court, U.S. Supreme Court.
Your employer has two distinct, (relatively poor) arguments. The first, is that you are an independent contractor and are thus exempt from withholding, overtime, meal and rest break rules, and a host of other restrictions and requirements. The second, is that you are an employee, but as an employee you are professionally exempt. Absent a written agreement, the second argument is somewhat ridiculous as the default assumptions of someone employed in California is that they are a non-exempt employee absent an employment agreement to the contrary.
While it is the employers job to prove that you are an independent contractor, to properly win your case, you will need to prove that you were in fact an employee.
Accordingly, to be best prepared, you will want to show that the employer had the "right to control the manner and means of accomplishing the result desired." This means you should try to bring as much evidence as you can to show that the employer had the right to control the work you produced. Additional factors to determine whether someone is an employee, or an independent contract are:
(a) whether the one performing services is engaged in a distinct occupation or business;
(b) the kind of occupation, with reference to whether, in the locality, the work is usually done under the direction of the principal or by a specialist without supervision;
(c) the skill required in the particular occupation;
(d) whether the principal or the worker supplies the instrumentalities, tools, and the place of work for the person doing the work;
(e) the length of time for which the services are to be performed;
(f) the method of payment, whether by the time or by the job;
(g) whether or not the work is a part of the regular business of the principal; and
(h) whether or not the parties believe they are creating the relationship of employer-employee.
S.G. Borello & Sons, Inc. v. Dept. of Industrial Relations, 48 Cal.3d 341, 351
In regards XXXXX XXXXX the argument that you are an exempt employee under the professionally exempt status, all you need to do is point to the fact that there is no contract setting out your exempt employee status.
Here is a good website which sets out the differences between the different types of employees and independent contractors and how to qualify under one of the above categories:
Hopefully this fully answers your question. If you have any additional questions, or if you need additional clarification, please do not hesitate to ask. Have a wonderful start to 2013.