Powerlines emit EMF, whether it is drops to your house or higher kV transmission lines. The RF issue lies with the failing hardware on those circuits. Insulators will emit strong RF if they are tracking, contamination of the insulating material as an example. Mechanical hardware on those circuits can also emit RF if components loosen/fail with age. This is a constant battle between power companies and those that under build communication lines off the same pole.
I recommend approach distances, not based on RF or EMI, but to keep you and your utilities circuits free of any incidental contact. People that survey powerlines are doing so with the utility's approval and have made hardware upgrades to reduce any influences. You, without approval, maybe seen as a threat to the system. Make contact and cause an outage, you may end up as the poster child example for what not to do.
Just use common sense when flying near powerlines.