As far as my Luka goes, i've never seen a female with the name. I've always thought Suka was a male as well just because i assume if he was a female it'd be more like Suki. I do however, like Elyse deal with most people assuming Luka is a girl. Whether or not this has to do with his name, i'm not sure. I think he's just too pretty
On another note, I deal with this issue regarding my name all the time. I've always been called Alex my whole life but when it comes to writing emails at my job or even chatting online here i have to write out Alexandra so people will know i'm female.