Dear Jason, I'm not a process server or an attorney, but I can say with some confidence, that the answer to your question is - NO. The whole idea of having someone served is that a person must accept the paperwork. A PO Box is not a person; and cannot sign for acceptance.
But, you may be able to request that the post office provide you (or the process server) with the address.
Process servers, and postal workers, if you know the answer, we would love to hear from you.