The two potential problems I can foresee is the quality of the bearings, and the construction of the rims. The bearings (if any), are likely of a very low quality that could be prone to self-destruction under the rigors of karting. Let's face it- pressure washers don't tend to roll at 30MPH or so. Many low-quality wheels are not constructed in such a way that they can take the sideloads encountered when steering at speed.
The tires might be okay.
If you toss up a pic or two, it should help us help you.