Oh, please! This solves the wrong problem. Suppose the rogue admin maybe wants to know who is paid more than him - well, if the encryption is a homomorphism the less than relationship (and the equals relationship) on salaries is preserved by the encryption (actually the equals relationship is preserved by any encryption where both the key and the seed is independent of the rest of the data in the row - something that people thinking of encrypting things like salaries, bonuses, tax codes, and so on usually forget even though "X is paid exactly the same as Y" may be information that shouldn't be freely available).
Anyway, homomorphic encryption is old had - people have been working on this for a very long time (since about 1960 at GCHQ I think, but of course none of that was published, certainly since the 70s at MIT) and there are partial results all over the place. If someone has come up with a workable and secure algorithm that's a nice piece of mathematics and it may even be useful in some contexts, but it's not really interesting so far as concealing information from the dba is concerned because it still reveals too much.