Whyte considers this to be a medieval variant of Old English Randolph/Randolf.
ONC suggests the name is Scottish from Old Norse "advice wolf".

The Rootsweb list of Latinised names separates them: Ranulf is Latinised to Ranulphus, Randolph to Randulphus. The closeness of these names suggest that there may be confusion in the older records, or in the interpretation of them.