The short answer to your question is YES. If you have ever taken anatomy or human health and reproduction, this would be covered in the textbook.
One word that might have you tripped up is "ganglion." In short, ganglion refers to a group of nerve cell bodies. The "pelvic splanchnic ganglion" is more commonly referred to as the pelvic splanchnic nerves.
These nerves generally start at the base of the spine and run down to the walls of the rectum. They are responsible for the control of the pelvic and genital organs. To put it bluntly, they tell the body when it needs to go to the bathroom (both functions) as well as control sexual functions like erections.
As for causing diarrhea when stimulated - I think that part might be a little contrived. In order to have diarrhea - you would have to start with liquid bowels. I'm also not sure there is a legitimate way to "stimulate" them in order to cause an instant reaction.