Its quite normal in racing (especially spec class racing where everything is the same, nothing different allowed other than drivers and suspension dial-in), Racing is not cheap, and that goes for the racers and the sponsors, but in a race series like this it allows a competitor to afford parts at a huge discount and allows an MFG to pimp their gear. Its actually kind of a win-win situation.
Look at Nascar, you only find Goodyear tires on cars. In Formula 1, you only find Pirelli tires. In circle track racing, only Hoosier tires. There are many other series that will only allow one tire mfg brand to be run on the entire field.