Regardless of the reasons for the origin of the use, "he" and "him" are correct when the gender is unknown or ambiguous. Other forms, no matter how common, are not good English.
Please take this over to the Language Log blog at http://languagelog.ldc.upenn.edu/nll, where linguists, i.e., professionals who know a great deal about things like English grammar and usage, will quickly disabuse you of this notion.
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