SS not sure if the question is still un answered.

some interesting read on murugan/kadamban - skanda/karthikeya rishi moolam....

http://karkanirka.org/2008/04/13/murugan1/

from what the authors has researched - murugan and skanda are 2 different gods--having their own identity in north and south .until the mash up arnd 4th to 9th ad happened.
take a look the blog also has link to the extensive research

please also read - http://karkanirka.org/2008/05/11/murugan1-2/ which claims murukan was much earlier to the vedic time(ie before the indus valley c and was worshipped as a spirit.