Does the end-to-end resistance of 37.5~62.5 kOhm mean that there is 25% accuracy in the MAX5422?

Yes, the MAX5422's end-to-end resistance can vary by 25% off the nominal value. For a particular MAX5422, the variance will be consistent for that device. For example, if the end-to-end resistance of a particular MAX5422 is 55kOhms, that device will always have an end-to-end resistance of 55kOhms. The max/min values stated are guaranteed by design, but you can expect the production devices to be much closer to the nominal value of 50kOhm. This device was designed for low temperature drift vs temperature change rather than end-to-end accuracy.

What is the factory default value of nonvolatile wiper position of MAX5422?

The factory default of MAX5422 is set at midscale, which is 25k. Please refer to the description of Nonvolatile Memory section on Page 9 of the datasheet (Rev 0; 7/04).