Nice catch on the radiation poisoning. Revised sentence:

I think that every uncertainty about a utility function is just a hidden uncertainty about how to weigh the different experiences that generate a utility function

Also

That is, the utility functions and their respective probabilities is not enough to uniquely identify the combined utility function.

This is 100% expected, since utility functions that vary merely by a scaling factor and changing the zero point are equivalent.

I think we're talking about the same thing when you say "adding preference uncertainty as an additional dimension of your ontology". It's kind of hard to tell at this level of abstraction.