I haven't taken the current OCA or OCJP tests, but I have similar certifications for versions of Java gone by. These tests tend to focus on syntax and the nuts and bolts of the language, while the Cattle Drive tries to teach you how to wield the language effectively. There is, of course, some overlap. The Cattle Drive would definitely help you, especially if you're new to Java and programing in general. However, I wouldn't go so far as to call it training for the certification exams.
It seems as though you are on a timeline. The Cattle Drive involves many messages between student and nitpicker. Each assignment can take a long time to complete to the nitpicker's satisfaction. Some of the assignments I completed took 10 to 12 attempts to complete and there might be 2 to 3 emails between myself and the nitpicker for each attempt.
It is not a fast process and cannot be done on a short time line. However the process of detailed conversations between the nitpicker and student is amazing. Where else can you go and receive one to one mentoring from Java Professionals?
I recommend the Cattle Drive even if it doesn't fit into you certification timeline.