The hull speed formula will still work with kayaks, assuming someone would take the time to come up with an accurate multiplier for that formula. The "1.34" number was derived experimentally with sailboat hulls I think in the late 1800's, so it's not real accurate for comparison with boats as narrow as a kayak.

There is a meaningful difference between kayaks and sailboats. Kayaks have a very limited power source, where sailboats don't. When there is enough wind to power a sailboat up to hull speed, there is often more wind than the boat can use, so hull speed is interesting and meaningful. It is not lack of power limiting the speed, it is inability to use the available power. Due to the need to stay upright in high winds, displacement sailboats are wide and heavy, and produce large wakes. The wave drag is the limiting factor for speed.

With a slender kayak, how fast you go is primarily a factor of how much power your body can produce. The boats are narrow and light and a powerful paddler can paddle faster than the point where the wave length of the wake is equal to the length of the boat. If they are narrow enough they don't need to climb up and over the wake, because it isn't very big.

So, the formula is exactly the same for hull speed because the formula is just a relationship between velocity and wavelength. On the water the velocity of a wave is about SQRT(wavelength) * 1.34. This really doesn't change between kayaks and sailboats, but with sailboats it has more of a relationship to top speed.

Some kayak designs will be more effected by wave drag and the "hull speed" will be more noticeable. A short, wide (more sailboat like) recreational kayak will only go so fast and you will quickly feel like you are running into a wall where paddling harder doesn't change the speed much. But as you get longer and narrower the wall becomes more subtle. I find that with my Night Heron design I don't really feel the wall but with the Petrel I do.

They are both the same width, but the Petrel is shorter and has more rocker, the Night Heron has a finer entry and seems to cut into the water more easily. As a result, at somewhere over 5 knots, incremental increases in power seem to create smaller incremental increases in speed with the Petrel than the Night Heron. The drag curve for the Petrel seems to rise more steeply and more suddenly than the Night Heron. It happens above a speed I am comfortable paddling for very long so it isn't a big deal, but it is noticeably different.

The Mystery is even narrower, with a much finer entry and more gradually curved shape and it never creates much of a wake and I've paddled it up to 11 knots (very briefly) without feeling that I was running into any hull speed wall. I was just not physically strong enough to power it faster and I got tired extremely quickly.