I don't know if elves--especially gods--have any such customs as a suitor seeking a father's approval. Espeically because, while Corellon does care about Eilistraee, their relationship is explicitly described as strained in Demihuman Deities (due to their different views on the drow and M.O.), so Ye'Cind having his approval wouldn't matter that much.
Back on topic, Ye'Cind sounds like an amazing companion for Eilistraee, but I'm really not sure about soulmate. Not because he has traits that would prevent him from being a soulmate, but because, even with the GH article, I don't have really a lot of info to understand, in-depth, what kind of person he is. We know he cares about the truth and about justice, as he dedicated decades to expose a murderer, and that he is a nurturer of arts and beauty much like Eilistraee. Both these traits would surely be a plus in Eilistraee's book, but... Idk, respect/admiration/affinity is not the same as being a soulmate. I must say that you're right, though; he definitely is a good candidate.
With that saide, while I acknowledge Ye'Cind as a good potential soulmate, I maintain what I stated at the beginning of this thread:
She's a free spirit, and can love with such freedom and spontaneity that I picture her being able to enjoy moments of intimacy, tenderness, or simply affection to their fullest without the need to bind herself to anyone.
When you live as long as a goddess, your idea of love changes, because like your perception of reality does. I picture Eilistraee as a goddess who can love many at once with intensity and unconditionally, and that the fact that she loves many doesn't diminish the value of her love for the single individual. Just like she does with the drow, she would love each for what makes them just themselves--a unique kind of love for each of them that comes from seeing the beauty that is unique to each of them, from knowing--and having shared, due to her choice--their dreams, their battles, and even the demons that they face.
I also think that the lines between romantic and non-romantic love would become blurred in many cases, because we're talking about a creature who can experience this sentiment is such a deep and spontaneous way, and who is *big* on freedom of expression, and one large part of romanticism and sex is that they are an expression of affection, among the other things.
Besides, IMO, Eilistraee can love deities and mortals alike (in fact, why would she--who chose to be one of her people--restrict herself to deities)?
Aside from that, even setting the soulmate matter aside, Eilistraee--as a divine artist herself--would surely love Ye'Cind's music, and to sing/play with him, or dance to his music. The two would obviously get along perfectly, so we know that she has at least good company.
Mathematics is the art of giving the same name to different things.
