We are using the Nordic nRF52832 and the nRF51822 in two different products. We seek to distinguish between these products and other BTLE devices with a scan using a dongle. Do these Nordic BTLE chips have a specific MAC address range? If so, what is the MAC address range for each?
The MAC addresses of all nRF5x devices are randomly generated at production and does not tell you anything about the device. You can use a different set of MAC addresses yourself instead of the default MAC address, but unless you do, the MAC address contain no useful information.
Is it possible to change the MAC address of nRF5x devices? If so, how does one do that? Is it written to a handle?
Yes, you can replace the default MAC address with any other valid address. You probably want to store your MAC address in flash during production, for instance somewhere in the UICR. Then you read it out after enabling the SoftDevice and sd_ble_gap_addr_set().
Note that the MAC address must be valid, though, so if it is not random you need to register a range. Perhaps an alternative could be to include some other information in the advertising packet that you can use to separate your HW versions?