I passed BEA's WL 6 test a couple of weeks ago.
The getgamma site is very good, except that it crashes all the time in the middle of practice exames, and should be your starting point. There are a few points to keep when using it:
1) There is a document called "Tuning WebLogic Server"
http://e-docs.bea.com/wls/docs61//perform/WLSTuning.html which is not in the getgamma site which you should read. It is short, easy to read, and most of the material in it is covered in other materials. However, it does have some stuff which is not covered in other places which was on the test I took.
2) This is a small point, but the getgamma site covers WL 6.0. BEA says that the certification exam is valid for both 6.0 and 6.1 but I had one question on monitoring where it said to select 3 and two answers were valid for 6.0 and three were valid for 6.1.
On the other hand, 6.1 has new stuff in other areas, like
servlets - I had no questions about this type of material. You probably do not need to study this stuff.
3) Almost all the questions in the getgamma site are pulled directly from the documentation. On BEA's exam most of the questions were pulled directly from the documentation but some were not. The only way to be able to answer these other questions would be to actually have written code and have hands-on experience as to how WL works. This second kind of question was maybe 10% of the total.
4) If you take the practice exam on getgamma many times do not trust your score on the section called "Configure, package and deploy EJBs, Servlets, JSPs , AND ENTERPRISE APPLICATIONS ". This section is pure memorization and there are maybe hundreds of possible questions. When you study the documentation after taking the getgamma exam you will tend to pick out the answers to those specific questions and get a high score on the getgamma site, but BEA will likely ask a completely different set of questions.
I know from experience that BEA's guidance in what you need to study to pass their exam is pathetic. I think even the exam objectives come from jCert and not from them.
I hope this helps.