In all honesty this is an over done argument, sure you can take a single great image with anything, there are shooters who only use a cell phone camera or Polaroid back in the day, but that does not mean a cell phone camera can do any job. I own a wide assortment of cameras of all kinds, and while I love shooting my own images with a "serious compact" I cannot think of many jobs that they could be my main camera, there is just a long list of things these cameras cannot do as well or a quickly as the "Pro" camera can do. I would never hire someone simply based on their equipment, but I would have to wonder about someone's professional commitment and ethics if they brought one Canon Rebel to shoot an event. I do not shoot weddings, but I am hired to shoot, and when I show up to whatever it is I am working on, I bring a minimum of 50% to 100% more gear than I need. Things break, cameras stop working, cards do not write, lights do not fire, lenses will not stop down or open up, meters stop reading, ac circuits get overloaded, the list is endless and everyone of these things and more have happened to me. When you are getting paid you need to come through, sorry to tell you but "Pro cameras" are pro cameras because usually they are faster, more accurate and a lot more reliable.
Many times this argument feels like a discussion of why Louis Vuitton Handbags are so much better than some other handbags, they are not you are paying for marketing, it is not same the argument with professional tools of any kind.
At the same time just because someone owns or uses professional equipment does not on its own make him or her a better shooter, talent is talent, equipment is equipment. I am sure there are a lot of boring incompetent "Pros" with all the right equipment, just owning does not mean you know what to do with it.
One should always discuss with anyone you hire what you expect and what they promise they will deliver, you work out the deal and hope for the best.