Hi 2MVAr,
1-If you havebalance loads,the system would work normaly even no grounded points any where .
2- If you have unbalace loads and multiple grounded points are there , the system would work normaly in condition that source neutral is grounded.
3- If the source neutral point is not grounded the system will work with floating neutral point ,it meanse the voltage will shift with respect to the loads impedace on each phase .
4- As I explained single phase loads would work properly if you have balance load on the three phase ,it meanse all single phase loads have the same impedance on different phasese .If not balance also they work but not properly due to shifting of the voltage and the loads may get damage because of the rising of the voltage on one phase and reducing one the other .