Leap attack : "This monster moves up to its Speed. During this movement, it may move through spaces containing enemy figures. Then, perfom an attack that affects each figure this monster moved through during this action."

a stone can be attacked but it's not a figure but an obstacle

My question : does an attack based on Leap, allow the Blood Ape go go through the stone space ?

No. As you said: the stone is an (attack-able) obstacle and not a monster (= enemy figure for heroes).

I thought so ....

Just get yourself the "Shadow Walk" overlord card. All set!