yup, It's hardware "agnostic". You can use whatever device and plug them in where ever.
The only required devices are the arduino ethernet shield, an arduino mega, and an RTC.
In some cases you will have to write code though like for an I2C device. The bit wise data is so different on each device that it's not possible to write generic code for it.
But for any digital or pwm or analog pins, it should be plug and play.