Releasing the prowlers also served another purpose. Since it was a test of survival, the first idea that would enter anyone's mind would be to hide. This would allow them to stay safe and pass the exam without fighting or anything that would harm their chances of passing the exam.
The other Examinees might not have been that skilled to locate and hunt down all these examinees who were interested in playing hide and seek. The prowlers, on the other hand, were creatures who had evolved to hunt others.
After being properly trained, they were able to hunt down those whose armours were still active. You see, the chest plate which was provided to the examinees was designed to leak a special scent recognisable only to the prowlers.
