When it comes to Tom Holub, he’s seriously talking about MUni. Other forms of unicycling, except basketball, are a waste of time for him. 
I used to be very into Track racing. Because that was the only form of unicycle racing, because unicycles only came in sizes up to 24". It actually made sense back then. But now, my main unicycles are a 36" Road machine and 26 & 29" MUnis, why would I want to pedal a 24" unicycle as fast as I can around a track?
Because a bunch of other people are doing it, at least at a uni convention, so it’s something to do. And I do still love the Obstacle Course, which is now called the IUF Slalom. Placed 3rd overall in that at NAUCC at the ripe old age of 51, probably with about as much practice as the two kids that were faster. But I used to practice it a lot.
My shoe of choice for Track was also what I wore for my other main discipline at the time–Freestyle. Artificial turf shoes. Those worked well for me because the ones I was using were lightweight, and had great tread for pedal and wheel-walking grip. I wore a lot of MacGregor Turf (or Golf) shoes, from Kmart. They were cheap, lightweight and worked well.
While ultimately you should seek a stiff sole, that only really comes into play during the first few seconds of any race. Flexible soles will dissipate your energy during hard acceleration, but once you’re moving it’s not important. At that point it’s all about grip, though grip has a lot to do with technique and training. Developing a good, high-speed spin.
Below is a picture from 1987 when I was trying to set a gliding distance record (about 8/10 mile). Good view of the turf shoe bottom, and the effects of gliding on it. Those shoes were Nikes, of course.
BTW, the pedals in that picture were my choice for racing back then; super-light Skyway Recreation pedals. Nearly weightless alloy shell, graphite/plastic body, steel spindle and no bearings at all. They worked, but more support for the foot would be better. Sometimes metal pedals are still allowed, but rarely if it’s a nice track.
