In some respects, no; and in some respects, yes. Yes in the sense that biographical resources can sometimes provide rich resources for understanding the philosophy of the person in question, yes in denying there is a rigid distinction between someone's own religious reflections and his philosophical comments on religious discourse. But no in affirming the following: that there is no rigid distinction does not mean there is no distinction. We do well to distinguish (a) between the following remarks about religious discoruse: "The forms of language are the forms f life." "There is a distinctive religious form of life with its own distinctive discourse" (philosophical remarks about religion), and (b) the religious remark "Human beings are corrupted with sin; if they are aware of that they are utterly wretched." Sometimes the latter-type remarks can help us understand remarks of the former type. (Perhaps it goes the other way around as well.) And sometimes it is unclear which kind of a remakr a given remakr is, e.g., "Religion is nothing more than the projection of one's emotions." But nothing but confusion will result if we do not distinguish these types of remarks, particularly in their paradigmatic occurrences. (p. 793)
Kai Nielsen, by the way, is one of the small handful of atheists who actually do philosophy of religion worth occasionally paying attention to; he typically does work on naturalistic ethics. Here you can find Antony Flew's 2002 review of Nielsen's work Naturalism and Religion (which actually sheds a bit of light on the hubbub about Flew this winter).