While there isn't any way to directly import characters from Saints Row 2 into Saints Row: The Third, the character customization for both games is very similar. But are they similar enough? Would using the same values for each customization parameter produce the same face? Do they even have all the same parameters?
After spending some time in Image as Designed in SR2 and in the SR3 Initiation Station, it's clear that you cannot create the same character in both games by using the same values.
While both games share nearly all the same customization sliders, the values are relative, not absolute. This can be most easily seen by switching ethnicities within the same game. Even with the same skin tone and all sliders set to 50 (the default), characters will not look the same if they were created from different ethnicities because different "bases" underlie your customizations.
Similarly, SR2 and SR3 use different bases, even for the same ethnicities. While it might be possible to create the same face in both games, they won't have the same customization values, making it impossible to easily "port" characters.