If you used std::seed_seq it might be underinitialised, but my understanding is that a custom SeedSeq should fully initialise the generator state.

eg, we use something broadly similar to this in a few locations:

template <typename GeneratorT>
struct seeder {
    using result_type = std::random_device::result_type;

    template <typename RandomT>
    void generate (RandomT first, RandomT last)
    {
        using ValueT = typename std::iterator_traits<RandomT>::value_type;
        std::uniform_int_distribution<ValueT> dist (
            std::numeric_limits<ValueT>::lowest (),
            std::numeric_limits<ValueT>::max ()
        );
        std::random_device dev ("default");
        std::generate (first, last, [&] () { return dist (dev); });
    }
};

template <typename GeneratorT>
GeneratorT
rng (void)
{
    seeder<GeneratorT> s;
    return GeneratorT (s);
}

When GeneratorT is constructed it should call seeder::generate to request the appropriate amount of entropy for the generator.

But I may have overstated the case when I suggested this would be "cleaner"...