The reset pin can't be used as a GPIO when it is enabled. When the reset pin isn't enabled it can be used like any normal GPIO pin. And all GPIO pins can be configured as interrupts.
From the infocenter: "Important: Pin reset can be enabled by defining the CONFIG_GPIO_AS_PINRESET variable in the project settings. This can be done by defining the preprocessor symbol in Keil, go to: Project – Options for Target – C/C++ – Preprocessor Symbols – Define. Here you can add the CONFIG_GPIO_AS_PINRESET variable after NRF52."
