Traditionally Orthodox are buried "green" anyway (simple coffins, no embalming, etc). I am told that in Greece and other Orthodox countries, the bones are usually dug up after a few years and kept in family ossuaries, so nothing remains in the environment long-term.
What might be un-Orthodox is not having a certain burial location (dumping the remains into a reef), because there is no place for family to visit and no grave for priests to bless or pray at. Of course, it's not absolutely necessary, but having the physical location is important and is possible in 99% of deaths. Also, marking the grave with a cross is a symbol of ultimate victory, while marking it with a tree or something else strikes me somewhat as a symbol of resignation.
So, to me, the green burial proper is great, but somehow obscuring the location of the grave is problematic. Burial in an Orthodox cemetery is ideal, because the body will still be involved in the life of the Church. At monasteries especially, the graves are frequently blessed and prayed over.