Does OAEP make sense for use in an ECC ElGamal cryptosystem? The way I see it, OAEP makes questionable sense even for RSA because even though it's a "all or nothing" transformation, many RSA ciphertexts already have to be split up into multiple blocks so that no one block exceeds the size of the modulus.
Yes, it can make some sense, and I've seen it in practical use. But beware that you can only encrypt very small plaintext and that's only after you make adjustments to the MGF-1 scheme to use a smaller hash (the leftmost bits of an existing hash, for instance).
For a generic cryptosystem you could use a large (512 bit) curve and use hybrid cryptography to get around the small payload size. But for a generic cryptosystem you are much better off using ECIES to accomplish the same thing.
I would only use El Gamal / OAEP if the ElGamal encryption has specific properties that you want to use.