Okay, first let me say that to some VERY small degree I agree with "the Spirit of God is at work everywhere it is allowed to work".  Yahweh by his spirit is in control of everything.  The best explanation for this comes from Romans 9:20-24 - "On the contrary, who are you, O man, who answers back to God? The thing molded will not say to the molder, "Why did you make me like this," will it?  Or does not the potter have a right over the clay, to make from the same lump one vessel for honorable use and another for common use?  What if God, although willing to demonstrate His wrath and to make His power known, endured with much patience vessels of wrath prepared for destruction?  And He did so to make known the riches of His glory upon vessels of mercy, which He prepared beforehand for glory, even us, whom He also called, not from among Jews only, but also from among Gentiles."

Because of His unlimited foreknowledge, Yahweh prepares ahead of time those whom he know will reject Him to still useful to make known His grace to those who will accept Him.  The Spirit of Yahweh will only be leading those who will accept His grace through Yahshua to Him.  That is where I draw the line in regards to the Spirit working in "places outside of Christianity".

Other than that, the gift of the Holy Spirit is only given to those who accept and are baptized into the name of Yahshua - Acts 2:38.  The Holy Spirit is only given to those who obey God - Acts 5:32 - which God do you think it is talking about obeying?  If anyone does not have the Spirit of Christ, he does not belong to him - Romans 8:9 - do you really think that Buddhists and Hindus would admit to having the Spirit of Christ within them?  Those with the Holy Spirit can say "Yahshua is Lord (or Master)" - 1 Corinthians 12:3 - do you think Muslims, Buddhists, and Hindus can say that?  Those of the true circumcision, with the Spirit of God can "glory in Christ Yahshua" - Philippians 3:3 - can any of the above religious groups do that? 

Malachi 3:6 - "For I, Yahweh, do not change;" - yet you seem to think that the "Spirit of God" who allows worshipping a cow (Hinduism) is the same one who wanted to consume the Israelites for making an idol of a cow at Horeb.  Maybe you are confused?

Can you honestly say that the same spirit is leading all the different religious groups on this planet?  And that the various forms of worship and idolism present in some of them, EXTREMELY contradictory in comparison to one another at times, is accepted by a God who says He changes not?

For one who stated that "as a Christian, I am grounded in scripture," your foundation seems to be pretty shaky.