The default firmware images from NRF use their development kit pinouts, so chances are if you use their code without modifying it then it won’t line up with the DK’s pinouts.
However, most peripherals in the NRF51, including serial, can be mapped to any pins. So you can look at our schematic and decide which pins to map the serial lines to in the sniffer firmware. https://github.com/bluzDK/bluzDK/blob/master/v2/HWDesign/bluzDK_schematic.pdf
And yes, once you have that you can just flash it to a DK through SWD and you should be good to go. Wiping out the internal flash is fine, all keys/IDs are stored on the external flash and won’t be lost, so just flash back through bluz firmware when you are done.