Yes, you can really make money with a dump trailer.  Dump trailers make money, period.  There is no other reason to purchase a dump trailer.  Or any trailer.  Make the trailer work for you and solve your problems.  Some people make money as part of their job.  Some people make money as part of their hobby (gentleman farmer).
You can make money with a traditional dump trailer.  Even better, you can make passive income with a dumpster business.