The couple of times I've tried using a dist pedal into a dirty channel I've not got a tone I liked, we play our dist pedals into the clean channels.
I ran a thread a while ago on how I was going to replace my ValveKing because I really didn't like the lead channel, but I bought a couple of Blackstar pedals, plugged them into the clean channel and got great tone. (dual HT, and a Dist X that Sue's nicked).
I see no reason why you can't use one in front of a dirt channel, but I think one or the other would have to be on a low gain setting or it will turn to mush as it did in my experiments, which I have to say I gave up on pretty quickly, so I probably missed something (or a lot).