Nero's relation in the sparda family is rather ambiguous, with one Scenario writer holding the opinion he's Vergil's son, even though the timeline and given ages makes this impossible unless vergil impregnated a human woman at 10 years old. Considering Nero's color scheme is infact red ble and purple(the coat actually is a navy purple, not straight blue) and Yamato glows purple in his hands, it's more likely, IMO, that he's actually a reincarnation of Sparda himself, the age timing would be about right for Sparda's assumed death no less.
On to Killing face...no, I doubt he's meant to represent this universe' incarnation of Nero. Nero's a human turning into a demon, Killing face is some random boss, and teh whol;e deal with Lilith's child seems like a bigger deal than that.