Grave Ohja's effect:

While there is a face-down Defense Position monster(s) on your side of the field, no player can select this card as an attack target. Each time a monster on your side of the field is Flip Summoned, inflict 300 damage to your opponent.

If someone flip summons Grave Ohja would his effect to do 300 dmg when a monster is flip summoned while he is faceup on the field activate?

Thanks.

im assuming you mean, would he do 300 for his own slip summoning....in which case no. because he has to be face up for the effect to be active and the effect wont be come active until after he is flipped summoned.