6.6 Voltages
Voltage must not exceed 75V for direct current or 50V for alternating current except where prior approval from the event organisers has been confirmed. Note that batteries may have a higher voltage during charging and care must be taken not to exceed these limits.

7.5 Maximum Cell Count (series) and voltage

7.6 Parallel CellsBatteries cells may be connected in parallel to increase capacity and discharge current. Caution must be taken with NiCd and NiMH as these cells may only be connected in parallel during discharge.

This indeed means that you could use 2 packs of 30 cell NiCds in parallel (total 60 cells). But you could not connect in series.