Here's the deal with the Candyshell and Bodyguardz. I have both (well, actually BSE, but same concept).
It DOES fit with the Bodyguardz, but not perfectly. What I mean is that the button covers - where the case covers the power button and volume buttons - will not align properly, so you will have to exert a bit more effort to push them.
Without the bodyguardz, the slightest effort will push the button. It's nicely designed that way, but with the bodygyuardz, it is much more difficult.
So, if you can live with that, then go for it. Otherwise, keep looking. I can tell you that the case that fits the best with skins, IMO, is the iSkin Solo.