Is it permissible to complete ablution by wiping the ears and feet if a greasy residue (cream or natural secretion) from wiping the head remains on the hand, and does that invalidate the purity of the water?

The persistence of a cream's residue (such as scent or an oily feel) on the hand does not affect the validity of ablution as long as it does not prevent water from reaching the skin. Similarly, the oily substances secreted by the body do not affect ablution.