I'm sure that it's possible, but Ive never done it.
John S
PDX OR

I have grafted Nigra and others to a I.E, but if this a large tree you might have a hard time keeping the I.E. competing branches from overtaking the Nigra limbs. At least that was my experience grafting other cultivars on a well established tree. Maybe with a younger tree better results.

Thanks guys. The IE is roughly 4.5-5" in diameter. I'm thinking of doing bark/rind grafts and some cleft grafts.