Supplying NTC by different voltage from VCC
You would not be bringing Vcc off the board, but Vcc through a resistor (perhaps 10K). Not the same thing at all.
You can add a ferrite bead to the ground connection to keep the 'antenna' from bouncing your ground around, and use shielded wires. Then filter and maybe buffer (if necessary) the signal before it goes to the ADC.
Edit: assuming your ground is earthed, something like this:



simulate this circuit &ndash; Schematic created using CircuitLab