I hope not. But I wouldn’t be surprised if they were. I recently had lunch with two former federal agents who now offer technical surveillance countermeasure services to the private sector. We talked about what they view as the perfect storm in their business, a society that has seen a steady decline in ethical behavior, and the relative ease at which sophisticated eavesdropping equipment can be obtained today.
Chances are slim a campaign, as a policy, would overtly spy on an opponent. What I think is much more likely are campaign staff or volunteers spying, without the candidate’s knowledge, to gain status within the campaign as someone with a shrewd ability to predict the opponent's behavior. People are always looking for shortcuts to get ahead. And in a campaign, coming forward with with consistently valuable information from a friend of a friend source will get you noticed.
Political spying doesn’t have to be all super-secret bugs and wiretaps. It can be as simple and low tech as getting the access codes for an opponent’s conference calls. Or planting a voice activated digital recorder at the opponent's debate podium to hear conversation between the opponent and campaign manager during breaks. If someone wanted to volunteer with a campaign to place listening devices, obtaining the equipment is frighteningly easy. A simple Google search using the search string site:eBay.com "hidden camera" returns thousands of links. Many of these devices are made in China, fairly good quality, and relatively inexpensive. They often come with free shipping and arrive within weeks.
Not really up for waiting. Try Staples, I took this picture of pens with a hidden video camera that also record audio at my local Staples store selling for $79.99.