History of Roman Catholic Saints
Some theologians believe that many people venerated as Saints never actually existed. The polite term for such “Saints” is ahistorical. Sorting out exactly which Saints are ahistorical is difficult, because of the larger difficulty of proving a negative: the absence of independent records of a Saint’s existence doesn’t prove she or he never existed; indeed there are no specific records of the existence of many people who lived before the 20th century. The Acta Sanctorum (hagiographical work) of the Bollandists forms a major part of the historiography of named Saints.
There are a large number of Catholic Saints with what appear to be pagan names. Most likely they were pagans who converted to Christianity and subsequently became Saints. However, it is possible that some pre-Christian deities (especially in Rome’s area) were accidentally adopted as saints. It is thought that some cults were “Christianized” in a fairly direct manner. The basis for this is usually a similarity of names. For example, it is now commonly asserted that Saint Brigid was based on the Celtic goddess Brigid. The goddess was popular long before Christianity reached Ireland. Another possibility is the melding of the actual life of the Saint with myths related to pre-Christian gods and heroes. There are some striking parallels to the events portrayed in the lives of certain saints and fables such as Androcles and the Lion.
http://www.catholicexpert.com/saints.html
Of course, that a general teaching can be applied in error is not in itself an indication about the truth of the general teaching, and the wonderful thing about these supposed sociological observations is their argumentative vagueness. "Some Catholics do icky or silly stuff" rapidly becomes "Catholics do icky or silly stuff," which is inches from "All Catholics do icky or silly stuff," which readily morphs into "Catholicism is wrong," especially when words like "exactly" enter into the fray but are used more for rhetoric than, ah, exactitude.
"Some" theologian believes virtually anything. That gets us no closer to why one would choose to embraced speculation designed to validate a particular prejudice rather than simply relying on the primary source material.
I do not disagree Doodus Romanus may have just switched his Santa Claus for St. Nicholas when he converted; what I want to know is why one would propose such speculation other than as a cynical attempt to undermine the faith of others when neither Doodus, nor anyone else, documented such a switch?