EK use an electronless('ish) process for their blocks nickel plating and if you look through the galvanic corrosion chart you'll see that nickel and copper are very close to each other. Corrosion can and will happen inevitably but not at the same rate as aluminum and copper will be in a similar loop. That being said you should follow up on the rest of the material covered in the watrcooling sticky(located in my signature space).
On my pseudo first watercooling build I went with a mixed and matched setup and hand picked each part from a varying degree of manufacturer's but the caveat is that my components inclusive of my rad are all copper. The good thing on EK's side is that they will offer you warranty if their nickel plating chip or...