I have been using a relay card from another manufacturer with almost the exact same design as that for the past month (except my input is active low), and I have not had any problems with the GPIO 5V output driving the coils or drawing and/or feeding anything bad back into the pi, although I don't dare turn all 8 relays at the same time (480ma through all the coils). I did discover on mine that between the active low problem and the fact that the 3.3V output of the GPIO pins was not enough to drive the optoisolator, I needed to use transistors to convert the 3.3V input to 5V and everything works fine now.