If the creature normally is allowed to make both weapon
attacks and natural weapon attacks as part of the same full
attack routine, the monk can do the same (making unarmed
strikes in place of weapon attacks). Since a centaur can make
two hoof attacks in addition to his longsword attack, a centaur
monk can make two hoof attacks in addition to his unarmed
strike attack (or attacks, depending on his base attack bonus).
The monk can’t use his natural weapon attacks as part of a
flurry of blows, but he may make natural weapon attacks in
addition to his flurry. Such attacks suffer the same –2 penalty
as the monk’s flurry attacks in addition to the normal –5
penalty for secondary natural attacks.