Keep in mind, as well, that while angels were often referred to as the "elohim" (and then there is that long debated passage regarding the nephilim), and the early, pre-Mosaic Hebrew religions might have believed in the existence of other gods, that the "I AM" who sent Moses quite clearly states in the first two Commandments that all other "gods" are subject to him, and that there is to be none above him. The early Jewish people may have believed that the "gods" of surrounding cultures might have been massing an attack upon the One, but the God of Abraham, Isaac, and Jacob demonstrated time and again his overall superiority. Starting from Egypt, where a god supposedly sat on the Pharaoh's throne, and then moving on to the wilderness, where the forces of the Baals, Molechs, and Chemoshes were arrayed in all their might, the LORD our God consistently proved his might. After the settlement of Canaan Dagon learned just how powerful this One is, and the Philistines carted the Ark back to a beaten people cause God kept making Dagon look silly.
Oddly enough, the surrounding cultures seemed to get the point better than the Israelites or the Jews. Time and again when the Chosen people would backslide into pagan practices and were conquered by others, the conquerors reveled in the fact that the Jews had abandoned their God, leaving them open to subjugation.
By the time of the Babylonian captivity the people finally started to get it.
Keep in mind as well that the other gods of the pagan religions during the start of Christianity were equated with demons by none other than St Paul himself (we'll save St Paul's other remark about idols being just sticks and stones for a later thread). There were also many interesting things going on in Hellenic philosophy developing it's own monotheism. To a pagan peer of Abraham or Moses pretty much any spiritual being could have been a god, spirits of the dead were just as good as "spirits" of fertility or commerce. By the time of Christ there were pretty much only three options for the Educated Man: pantheism, monotheism, or atheism.
Our relatively recent culture has started disbelieving in the existence of anything spiritual (though we seem to be emerging from that "phase"), so the idea that the Hebrew weren't strict monotheists from the first can be a little faith-shaking. Regardless, from the first pronouncement to Moses on, the Hebrews knew the "I Am" our God is One, and that there is none higher.
As for the salvation of Abraham, Isaac, and Jacob, well, "Abraham had faith, and this was counted unto him as righteousness". Despite any heterodox opinions Abraham might ("might", remember that) have held regarding the existence of other gods, he followed his (and our) God above all else.
And for the salvation of "righteous" pagans... well, it's not an Orthodox source, but you cannot worship Tash with righteousness. Whatever the name that might come from one's lips in prayer, one's deeds proclaim much more the devotion and to whom it is given. (this is, of course, no escape route for those who learn of Christ and deny him).