I talked with a pilot who does fly a 500 for one of the US companies that does this work. As far as he was concerned, powerline patrol was more dangerous than what he does. This was confirmed at the Last Heliexpo where I talked with several management pilots and linemen for companies like Winco, Wilco Construction, Haverfield, Bonneville, etc. Everyone of these companies have a very strict SAFETY FIRST policy. Nothing happens very fast. The procedures are set in granite, not just stone. Things like the above course and other required training programs. Most of the powerline patrols are run done by contractors who were the lowest bidder, so they tend to push speed and get it done NOW. And you can see the results.
Of course none of this is as much fun or as interesting as running the powerline saw. Yee Haw!
As for wire pulling, forget the Squirrel. Go with a Lama and go big early.