Dryer vent pipes touching copper hot water pipe
This is not likely to be a major problem, but I can think of two ways it might cause trouble. One is noise, which can occur when the pipe moves due to thermal expansion or rapid water shutoff. Another is galvanic corrosion, which can occur when non-copper metals contact copper water pipes.

Either of these issues can be easily addressed by placing a section of foam pipe insulation around the copper pipe in a way that prevents contact with the duct.