It depends what you mean by "leg work." In terms of strength training, I'd say no because to develop strength and mass you need to overload the muscle (that is, add weight). I would think cardio work would provide endurance benefits to the leg muscles, but only until your body adapts to it. And I don't think it would be comparable to the unweighted leg work you'd do in, say, Butts & Guts. In my opinion, you need to train the legs separately from the cardio work. Although you can certainly get some cardio benefits from doing a good leg routine.
That said, if your legs are fried for any reason, skip the leg workout for a day. If you're just a bit sore you should use your own judgment.