Yes, and I've installed one myself. The only thing you need to watch for is the bottom most ram heatsink. It will get in the way of the Accelero heatpipes. If you offset it slightly, or use a shorter ramsink like those from Zalman, the heatpipes will clear it and you get proper seating of the main heatsink.
You'd also be wise to get some aftermarket ramsinks as well so you can put them on the VRM's. You can use the included VRM sink that comes with the Accelero, but it's made for a different model of video card, and mine took a fair bit of modification with a fine-bladed hacksaw to make a workable solution.
How are the temperatures if just using the accelero passively on the 4870? I was thinking of getting one and using it passively, but modifying one of my case fans to duct air over it, which I can turn on in games and turn off when its not under load.