Given that it should be hashed before it even hits the database I'd sure hope that it's hex by the time the database sees it.
Let's take hashing as implied, at this point. 🙂
In regards to web app knowing the difference, I did some testing and I can confirm that C# absolutely does see the Emoji differently than plaintext, and does generate an entirely different hash.
Oh good, then maybe - and I hope this is the case - I'm wrong.