Doesn't look like that value is used at all.
Code:
// iterate through our defensive procs and try each of them
for (int i = 0; i < MAX_PROCS; i++) {
if (MakeRandomInt(0, 100) < MakeRandomInt(0, 20)) {
ExecWeaponProc(DefensiveProcs[i].spellID, on);
}
}