Let me start with the most recent points and move back.
It's likely important to understand something about 'El' - a point I shall come back to. It is now realised that the background to Israel is to be found in the native peoples of Palestine, often referred to as Canaanites.
I'm using Wikipedia for convenience, I don't think that scholastically, too many people would quibble over the following entry, discussing the deity, El.
ʾĒl (written aleph-lamed, e.g. Ugaritic: 𐎛𐎍, Phoenician: 𐤋𐤀,[1] Hebrew: אל, Classical Syriac: ܐܠ, Arabic: إل or إله, cognate toAkkadian: ilu) is a Northwest Semitic word meaning "god" or "deity" and it is used as the name of major Ancient Near East deities, including the God of the Hebrew Bible.
In the Canaanite religion, or Levantine religion as a whole, El or Il was a god also known as the Father of humanity and all creatures, and the husband of the goddess Asherah as recorded in the clay tablets of Ugarit (modern Ra′s Shamrā—Arabic: رأس شمرا, Syria).[2]
The bull was symbolic to El and his son Baʻal Hadad, and they both wore bull horns on their headdress.[3][4][5][6] He may have been a desert god at some point, as the myths say that he had two wives and built a sanctuary with them and his new children in the desert. El had fathered many gods, but most important were Hadad, Yam, and Mot
Reference: http://en.wikipedia.org/wiki/El_%28deity%29
the entry continues: Cognate forms are found throughout the Semitic languages. They include Ugaritic ʾil, pl. ʾlm; Phoenician ʾl pl. ʾlm; Hebrew ʾēl, pl. ʾēlîm; Aramaic ʾl; Akkadian ilu, pl. ilānu.
In northwest Semitic use, El was both a generic word for any god and the special name or title of a particular god who was distinguished from other gods as being "the god".[7]El is listed at the head of many pantheons.
A lot of material has been found dealing with Canaanite religious beliefs and if anyone is not familiar with this material, a good essay to background El, may be this one:
Canaanite Myth and Hebrew Epic: Essays in the History of the Religion of Israel
The author is Frank Moore Cross Jr. who was the Hancock Professor of Hebrew and Other Oriental Languages Emeritus at Harvard University. (now deceased).
Some prior post on this site by Leolaia will also provide some profound thoughts.
Boyarin alludes to 'El' and his associated god Ba'l, as ancient ideas in Israelite thought, and suggests that they may be the pattern for the vision that the author of Daniel claims to have had. Boyarin cites an ancient text (for which I did not keep a reference).
"Ba'l comes near in his shining storm cloud. 'El is the transcendent one"
Whatever actually was the case in the past is always subject to discussion. Some say that the deity (God, Divinity) Baal, the god of war, became the Yahweh of the Israelites. I cite this to demonstrate historically Judaism developed from its Canaanite background with some different ideas about "God/El etc. But were the original ideas entirely forgotten? We may never know.
My personal view, is that there is another possibility for second god-like figure in the Daniel 7 vision. In the fourth century BCE, Alexander the Great conquered the Persian Empire, which had included the Palestinian home of the Jews. Greek colonies were planted all over the empire. Hellenic thought diffused throughout the empire, from Greece down to Egypt and from the Mediterranean seacoast east to present day Afghanistan and the borders of India.
If you're not familiar with that process of Hellenic colonisation, may I suggest Elias Bickerman's, "The Jews in the Greek Age." or Lee I. Levines, "Judaism & Hellenism in Antiquity, Conflict or Congruence."
I'm suggesting that the model for the Daniel vision of two God's, one senior, one junior may be found in the Greek Pantheon where Zeus was the chief divinity, but there were others who were still 'gods' but subject to Zeus. For example, Apollo, the Greek God of healing and prophecy has been suggested as a pattern for the Jesus figure. Or, maybe Dionysus, the only Greek God to have a human mother.
Whether either or neither of those two possibilities is right is likely beyond proof. All we know for sure, is that likely in the second century BCE, an unknown (probable) Jew wrote a story about a divine figure, the Ancient of Days (the English word 'divine' can be used, as the figure is evidently a God who arrives in typical Jewish fashion0, coming to sit on his throne and issuing a royal/divine command that another god-like figure, called the 'son of man,' also coming in the clouds of heaven and being given royal privileges over everyone on the earth,
It is being argued that one 'God' is higher, than the other 'God,' and therefore it is not polytheism. That must be a failed argument. Why? Because in most polytheistic pantheons there is a 'senior' god, and one or more Junior 'gods.' The Graeco-Roman Pantheon has already been mentioned, as well as the Canaanite example, and for good measure we could add the Hindu example, where Vishnu is often cited as the chief God, though he may have a bit of competition.