St. Maximos the Confessor, compiled in the Philokalia Volume II, pages 180-1.
Can you tell me where the Spirit is not?
Most accept the distinction between 1) the Spirit and sacramental grace, and 2) the Holy Spirit existing everywhere. Obviously the Spirit is everywhere and "fills all things"--the universe would cease to exist if the Spirit didn't sustain it. But whether the Holy Spirit makes Catholic sacraments grace-filled, or Methodist fruit juice, or is in Gnostic crackers, or Wiccan... well, you see where I'm going with this...
EDIT--Though looking back, maybe this isn't relevant to you comment. Sorry about that!
What is grace but the working of the Holy Spirit in us? If St. Maximos believed that the tendency for barbarians and nomads to settle and become civilized, setting aside their, "savage laws which they had kept among themselves from time immemorial," was the work of the Holy Spirit, is that not the same as saying that they become civilized by grace? I don't think that we can be so quick to put the Holy Spirit in a box, and claim that we are exclusively capable of interacting with it, as if it were some sort of magic, accessible only to the Church. The Holy Spirit is a person (and God for that matter), not a slave of the Church.
Is a Santeria chicken sacrifice sacramental like the Eucharist? Of course not! But if the Holy Spirit can work with barbarians to teach them of law and civilization, cannot the same be done by the Holy Spirit with Santeria believers and God? Of course, we know that we have the truth, and we should always try to bring those who follow false religions to Orthodoxy, but I don't think that we can be so quick to dismiss that God is working in others who truly seek after Him, even if they do not yet know the truth. I could be totally wrong about this, but I just don't think we, as the Church, have the capacity to put God in a box and dictate how He works; He is the one who tells us how we work, not the other way around.