It was surprisingly easy for Kain to be granted entry into the relic.
He had thought that they would intentionally infect him with something in order to see if he truly was resistant to whatever was in the relic. However, there were no tests or even any verification about what his contract was.
In fact, as soon as he signed up his name, after some back and forth with someone through the phone, Kain was approved and even given an ancient looking bracelet that supposedly would help prevent infection. A lower grade version of Serena's enchanted necklace.
Kain suspected that certain members of the faculty had an idea about what he'd contracted. After all, when he was taking up the Black Mission, he had to kill that test mouse using Bea.
From that moment on, Bea was probably on their radar.