Yeah, there's probably a global event you could use that provides the npc that was killed. Then you could just: (pseudo-code, not actual Perl)
Code:
if ($npc->GetRace() == 458) {
orc_global++;
}
elif ($npc->GetRace() == 524) {
gnoll_global++;
}
Those are the race numbers for the new DoD+ orcs and gnolls. Could put in checks for the old ones if you use 'em instead, or for any other race, I would think.
Not sure which event would work best, though, that would provide the $npc and $client that killed 'em. Maybe someone else can chime in.