My understanding is that all things are sustained by the grace of God. I know in Catholicism, grace is taught as being a created relationship - thus there are the "graces" (in the plural) which God gives to men to "do the right thing", and the "habit"/state of grace, which is an ongoing condition. Besides being purely creaturely, the other distinguishing thing about the RC idea of grace is that it pertains solely to the relationship between God and mankind (or at least to rational souls.)
In Orthodoxy, grace is still benevolence - but it is understood to be an energy and to be uncreated - that is to say, it is a participation in the glory of God in truth, and not simply in theory (since Catholicism would say the same thing, that grace is a participation in the life of the Trinity - but this cannot be if it is a created habit or series of helps, since God is uncreated). Also, it extends to all of creation - even the little animals and the trees are beneficiaries of God, hence of His grace.
The big distinguishing difference between a genuine member of the Church of Christ (Orthodox Church) and other men and creatures, has to do with the way this benevolence of God towards all things operates in the Orthodox. Before the time of Christ's Advent, there were worshipful, pious men, who were beloved of God and loved God in return. They beheld miracles, saw visions of grace, etc. Yet this grace worked upon them (if we can put it this way) in an "external" manner. OTOH, when someone is buried and raised with Christ in Baptism and become members of Him, this grace not only reaches deep inward, but will even find it's source within - they will become fountains of living water, even overflowing onto others. This mysteriological/"sacramental" grace, is given and nurtured by the Holy Mysteries of the Church, and is unique to the Church of Christ, the "ark of salvation".
I make these distinctions (between the Latin and Orthodox understandings) for the simple reason that while one could say in regard to both "yes, grace is gratuitous" - if by this one means it is something that ultimatly is unmerited by created beings), in either case that "yes" has different implications. In Orthodoxy, to say "grace is gratuitous" has implications not just for mankind, but for all things.