Well, I don't know exactly what you're talking about but I basically imagine one of two things:
A) the .swf import is referencing a specific filename and/or folder path, which means that it won't find the hair file if anyone else has changed its name or saved it in a different location than the modder had planned. (edit: part of me doubts whether or not .swf has the ability to reference other files. I'm not an expert on these things.)
B) there's no guarantee that an .swf import has any hair in it.
Either way, I don't see why you wouldn't be free to import a hair .png if the .swf doesn't load hair.
It would help if I knew which imports you're referring to, though, so that I can at least see for myself whether or not they should or should not have hair (and see if the hair is really not loading for you, or if you just aren't seeing it because it isn't there).
