View "Official Aramaic" as a diplomatic language, similar to English and French today. The Assyrian, Babylonian and Persian Empire incorporated different nations and a standard communication medium was needed. Because of the wide spread of the empires, different vassals would also have been appointed to rule the different city states, e.g., Darius the Mede. As was brought out by Bobcat, he could have been any of a number of historical personages, even Cyrus himself. If appointed by Cyrus, he would have ruled under him, and secondary rulers received secondary honors.
Bottom line is, you cannot use words or a language to date a document. Many scholars have tried (and failed). As seen, Official Aramaic existed from 700 - 200 BCE, so the Aramaic or loanwords of Daniel are not good indications of provenance or time of writing. I like Doug's suggestion of chiasms. That would explain a lot of conradictions in the Bible. Also, as was mentioned, many editors were involved in the construction of Daniel, the end product might have been compiled much later.