The question is VDD ramp time and RC-net time constant, given values from above example (C=0.1u, R=10k), 1.6 ms soft-start time from main DC/DC VDD power supply it will take about more than 1 ms to get PU_CHIP voltage above 2.0V:
Do you suppose, that something could go wrong in this case? I doubt it.
Reset supervisor in mentioned Bluetooth module is quite good decision, but in my case there is no space on board for it and I have no wish to pay for it. ;-)