Not 100% sure what you are thinking of doing.
When a PIC (PICAXE) is powered, an OC input will float. A floating pin can "float" up and down between 0v and Vcc. More often than not, it will follow the local mains frequency. It will not go much above Vcc due to the internal clamp diode. When not powered, it will be clamped to 0v by the same diode. If it is not powered and and a logic high is applied to the pin, current will flow to its Vcc pin and power the device parasitically. This MAY cause damage.
SOME ADC pins on SOME PICs are an exception to this but I cannot remember which ones. The PIC datasheet will answer that.
Is that what you wanted to know?