Can MAX30102's VLED+ run on 3.0 volts? Can VDDIO be 3 volts or does it need to be shifted down?

We cannot guarantee 3.0V will work for VLED+ in all parts if you use both IR and Red LEDs. There are part to part variations on the nominal LED forward voltages that may cause things not to work at 3.0V.
 
If you only use IR, 3.0V should be OK. However, since we did not characterize this and we do not test the part under that condition, we cannot guarantee it. We can only recommend what the datasheet says, which is a lower limit of 3.1V.

The I2C lines can be pulled up to 3.0V -- no need for a level translator.