MUX output amplitude level
When ...

a) the input voltage is within the range Vcc to Vee  

b) there is no current being passed between the selected input and the output terminal (the switch has an on resistance of a few 10s of ohms)  

c) you can neglect the very small amount of leakage current that appears in the switch (the data sheet gives a max of a few uA over the full temperature range, typically it will be much less, and much less again at 25C) 

d) the select and enable logic lines are between GND and Vlow, or Vhigh and Vcc, where Vlow and Vhigh are the logic threshholds for the chosen Vcc (usually 0.8v and 2.0v for an HCT part, 0.3*Vcc and 0.7*Vcc for an HC part respectively). If the logic is between Vlow and Vhigh, the switches may not turn fully on, or several may turn on. If the voltage is outside GND and VCC, then extra leakage current may be injected into the switch.

then yes, the output voltage = the input voltage, regardless of Vcc.