Technically yes it is, the major reason not to use the Calls in greyhound racing was an is because of the bias in the person recording the "official" calls, especially the "jump" call, calls in greyhound racing if used need to be corrected track by track

But back to your original question in horse racing they might just be discrete? Or maybe even poorly sampled (or poorly measured!) continuous data? If you throw calls in the discrete category, then it's perfectly fine to do averaging. And the same would go for poorly measured continuous data.