It should be just as secure: not revealing the AES key you use to encrypt data is about the same as not revealing the seed of the random number generator you use to randomly generate ids.
(In my unqualified opinion,) I don't think this qualifies as security though obscurity. It seems to be just as secure as using AES for encryption: a secret key produces a ciphertext that an attacker can read, without being able to decrypt it.
This doesn't sound like a good choice. It's security through obscurity.