Some utility functions can be found by randomly putting agents into various universes and seeing what happens

Implicit utility functions can. Explicit utility functions could not be computable, in the sense that you can go around saying that you want to put rocks into piles of sizes corresponding to programs that never halt, but what you'll actually be doing is putting them into sizes corresponding to programs that you think will never halt (either ones that provably don't, or possibly ones that pass some heuristic).