Kant categorical imperative simply seems to me a rational founding for a Christian ethic. As this is the centre-piece of his moral philosophy, it seems to me he is at least morally a Christian Philosopher. Of course this should not be surprising as his religious affiliation is as a Pietist - but I know that I would have found it surprising when I first started off in philosophy; as his denotation as a philosopher (to my mind at least) separates his thinking from Christian theology and morality.
Should one really call him a Christian philosopher in the same way for example one calls al-Ghazali an Islamic philosopher? (It may be of course untrue that Kants moral precept is Christian-like and that I have simply misunderstood the nature of the categorical imperative).