Evga is providing the product themselves. Why would this void warranty. From what I have heard Evga is more lenient in this kind of stuff. As long as you return it with the original heatsink-fan when RMAing the GPU they accept it apparently
As long as the manufacture states it is acceptable to remove the cooler, it's fine. I know for a fact EVGA cards' coolers can be removed WITHOUT voiding warranty. The only requirement is that you keep the stock cooler and re-attach it before returning the card for an RMA, Trade or other service.