Mmm... Yeah, that's a tricky one to get a straight answer about. But generally, cardio to lose weight and strength for strength gain. On the one hand, strength training indirectly supports weight loss due to increase in metabolism and making the body a better fat burner. On the other hand, for direct weight loss, cardio is essential.
I'm guessing, you want to know if you can sustain a cardio routine without compromising gains from strength gains. As long as your getting adequate fluids and proteins, it should be sustainable. Unless your into doing over an hour a day of cardio. Maybe that's the exception.
I not too clear on this myself, I hope more people answer this one.
On a side note, if you want a combination of cardio and strength training, try Capoeira.