Randy,
AREF is an input only pin, for providing a more stable (or non-standard) voltage reference for the ADC measurement systems (analogRead() calls). The datasheet for the atmega328 warns that a high-Z meter can be used to read the AREF pin, but to otherwise only use capacitive loads. The documents are silent on what might happen if one were to use the AREF pin as a current source for the tuning pot...I'd suspect that at best, the ADC measurements controlling the tune funciton would get squirrelly.
r/
Chris
Christopher Horner