The operation of a voltage regulator, in simplified terms, is like this:
1. If V < Vref, send more current to the output
2. If V > Vref, send less current to the output
So if you put two regulators in parallel with slightly different Vref values, the one with the highest Vref will win. Assuming it has enough capacity, it will send current to the output until the voltage rises to its Vref value. The other regulator will see a voltage that is too high and so it will reduce its output current to zero.
If you increase the load too much, beyond the capability of one regulator, then the voltage will sag until the second regulator cuts in.
You will not get equal load sharing between the regulators unless you put some resistors on the regulator outputs.
If there are no resistors and both regulators become active, there is a possibility of oscillation as each regulator will see an active load with unexpected feedback from its control actions. In practice I don't know how bad this could be.