Citing draft papers found on academia.edu
In my experience, absolutely anything can be cited, but not everything should be cited. Papers uploaded to Academia can often be what's called post-print, i.e. they are the version that has been peer-reviewed, accepted by a journal but not copy-edited by the journal [this is the point where the article still belongs to the author, after copy-editing it is the property of the publisher]. In this case it would still technically be a draft, but quite a long way down the line. 

Of course the paper can be cited, as long as there is enough evidence that the research is of good quality [if it's been accepted by a journal then it generally would be]. Things that should be cited are works like academic books, journal articles; whereas things like Wikipedia should not. Then there are grey areas such as drafts and online articles: basically if you know the researcher and field, and you trust the quality of the research, I see no reason not to cite it and include it in the bibliography.