Being a professional stock video contributor for years and using mostly DSLR video/photo camera for making video footage, we can deny any statements that you need a professional video camera for work. The magic of DSLR video/photo camera is versatility and agility, while you stay unnoticeable when making new stock clips in public.
It is possible to earn money from almost any camera, but there are a lot of technical problems with most low cost equipment. You can even shoot some stock footage with newest iPhones and Android phones, because they have many manual options for shooting video. But you can’t expect that every footage you make will go through stock agency currator filters. Technically perfect properties are important. Even if clips are very creative works. And this is where “any” equipment looses against more expensive.
Today it’s not just camera that matters. You need to add value to your footage. That is why extra equipment is in many cases needed. Good dolly sliders are cheap to get and even small jib cranes are not expensive anymore. Then there are underwater housings, gimbal stabilizers, aerial drones, slow motion cameras… Never ending equipment options that of course cost more money.
What we learned is, that investing never ends and it’s a must do if you want to improve. But there is a limit to it, so beware that you don’t become wasteful. Invest time in researching video industry and spend wisely. Once you’ll be living from making stock footage, you’ll need to calculate your living costs too.