Most people do use two different tires. Even if you get the same tire, many of them are designed specifically either for the front or the back so even if you buy the same brand and model of tire, they may be different.
The forums and reviews are rife with examples of running brand x model y width z up front and brand a model b width c in the rear. The reasons vary, but trail conditions and riding styles seem to be the main factors.
Need to make sure the frame can accept the width of your new one.