Can hash functions be used to transfer and hide ciphertext?

This somewhat similar locked question, "If cryptographic hashes are completely unique, could they theoretically be used to transfer data?", received several cogent no answers, but consider this:

Alice and Bob share a secret:

/p68J5gd3%}"jd9fkg;BtiAraGgsioe2:L<76e7emOngehf]jfur80}{_kod*6

Alice adds her ciphertext to her copy of the secret:

/p68J5gd3%}"jd9fkg;BtiAraGgsioe2:L<76e7emOngehf]jfur80}{_kod*6JWHSM

Now she hashes (secret + message) with SHA512 and sends the hash to Bob.

Bob knows that he has to do a bit of computation and find the ciphertext that will concatenate and resolve to the hash value he has been sent by Alice, and he knows how many characters there will be (5 in this case). So, in effect, Alice sent Bob a message he could not immediately read, but he can resolve it. They want to defeat certain aspects of traffic analysis, and they suspect that Mr. Attacker might be able to make easy preimage attacks on every hash they send--to which they respond "So what?"

Can hash functions be used to transfer and hide ciphertext in this unorthodox, expensive manner?