Hi Jason,
For the Adult LO206 categories, at this time the answer is no, there is not a spec rain tire. However, the dimensions of the rain tire must remain within the dimensions specified for the category (4.5×10-5 front, 7.1×10-5 rear).
Common rain tires used include the MG / Evinco rain, Hoosier rain, Mojo Rain, and Bridgestone rain. Many karters regionally have a set of rain tires that sits in their trailer with little to no use. That isn’t to say that having a set is pointless! Far from it! However, this is the reason why we don’t currently spec a rain tire, as it is so rare that they are used.