Because the divider output voltage is proportional to the ratio Rx/(Rx + R0), it's not linear in Rx respectively temperature. In addition the non-linear Pt characteristic has to be considered, as you mentioned. Nevertheless, using a simple ratiometric RTD "signal conditioning" circuit is a good suggestion for an ADC frontend, because it reduces the number of sensitive components considerably.
But for acceptable accuracy, Rx has to be calculated from the measured voltage, which involves a divide operation. For correction of the Pt characteristic, either a polynomial or a look-up table based interpolation gives good results. Analog Devices AN-709 presents C code and a table code generator for the latter.