I'm not that familiar with the 89C51, but reading the datasheet suggests that wouldn't be the case. It would however tie up the timer/Counter 2 as a clock generator so you couldn't use it for other things. It is possible to use Timer 2 as a baud-rate generator and a clock generator simultaneously, but the baud-rate and the P1.0 frequency would have to be the same.
But my main point was not to connect anything else besides the crystal and it's cap to pin 19 of the 89C51.