Scar and Mufasa are brothers,neither one of them is Nala's father. How seriously could the producers have meant it if they stated Roger Allers being the father after that.
And you guys keep forgetting that there aren't real lions,especially not regarding the community. These lion 'marry', I don't think real lions do that.

With that,her father can only be a rogue. Because if you look at it logically,you have the main characters, if there was any relation going on between them, it would have been mentioned in the movie. Such an important thing wouldn't be left out. So that leaves me to the conclusion that only a rogue or an unmentioned lion is Nala's father.