It varies by country: in some traditions, doctoral exams are big public events; in others, small private affairs.
At my University, doctoral exams have a chair -- someone from outside the subject who observes, trying to ensure that the process is fair and the regulations followed. Because of this, I have experience of a huge number of doctoral exams, many outside philosophy (let's see, a few from botany, entomology, economics, forensic science, psychiatric nursing, biomechanical sports science, etc.). They are surprisingly similar in the pattern of questioning.
Whether they are superior to courtroom cross-examination, however, is moot. This is because the purposes of the two practices are different: a court wants to establish the truth of X (or at least the appearance of the truth of X); a doctoral exam is frankly not interested in the truth of the content of the thesis, but rather in the validity and professionalism of the research and thinking that went into it.