Short Answer: No, this is NOT advised.
Long Answer: Doing surveys in the rain is both a safety hazard for persons operating the equipment and most often leads to survey problems:
1. The risk of shock from wet equipment: Possible shock hazards from batteries (12V), generator (120/220V 50/60Hz 10A) or power cables, resistivity cables (400V/2A), the instrument or anything near these items are more likely in wet weather.
2. Increased risk of lightning strike: The cables attract lighting and channel the strike back to the instrument. (Which is often where operators will be standing!)
3. Collecting noisy data and/or damaging the equipment. Rain percolating through the near surface may cause enough charge imbalance in the ground to create significant SP noise compared to non-rain days. Though most of AGI's hardware is weather-resistant, it is not weather-proof.