Since iddqd works on structured data, the model-based tests (while not being coverage-guided) do a lot of the kinds of things fuzzing would do against an algorithm which accepted unstructured data. In principle the bitstream from which structured data is generated could be provided by a fuzzer rather than the system RNG, but proptest makes that somewhat inconvenient. It's possible the newer Hegel library makes that easier, though.
(You're welcome!)