Yes, a spread spectrum clock can be used for 66.66 Mhz DDR clock. Please refer to below table for details:
Spread Spectrum Clock Source Recommendations
Parameter Min Max Unit Frequency modulation — 60 kHz Frequency spread — 1.0 %
According to the P1023 ballmap, V21 is the GTX clock pin of TSEC1 and T19 is the GTX clock pin of TSEC2.