I couldn't find any official documentation, but I did find that this topic was often mentioned in LEEDuser:

• Baseline for Ventilation Fan unconditioned space?
• Ventilation as Process Load
• the fan power of mechanical ventilation
• ventilation of unconditioned warehouse
• Mechanical Ventilation in some areas of building

According to them, the ventilation fan power in unconditioned zones should be treated as a process load and the ventilation fan power in the baseline case should be the same as the proposed case.

Any load not defined in ASHRAE 90.1 Appendix G appears to be treated as a process load.