Well, yes.
Although I would also consider this conclusion to follow from the broader claim that if A is a superintelligence with respect to B, B cannot control A, regardless of whether there's a true code of morality (a question I'm not weighing in on here).
Well, unless you want to say that if A happens to want what B wants, or want what B would want if B were a superintelligence, or otherwise wants something that B endorses, or that B ought to endorse, or something like that (for example, if A is Friendly with respect to B), then B controls A, or acausally controls A, or something like that.
At which point I suspect we do better to taboo "control", because we're using it in a very strange way.
Just a minor thought connected with the orthogonality thesis: if you claim that any superintelligence will inevitably converge to some true code of morality, then you are also claiming that no measures can be taken by its creators to prevent this convergence. In other words, the superintelligence will be uncontrollable.