I don't know what you were told about hiking the Samana peninsula and camping out at night, but based on my 15 years living in Samana, I certainly would not advise it. A single gringo hiking along the shore and sleeping there at night is at risk any place in the country. The danger is not that you will be attacked by hardened criminals from Santo Domingo, the danger is a poor Dominican with a machete who sees an opportunity to get some much needed money from someone he knows, being a gringo, has a lot of it.
There have been numerous reports of one person or a man and woman stopping to swim and sunbathe at what appeared to be a delightful, secluded beach only to have their vacation ruined by a campesino or two with machetes that came out of the bushes and threaten then in order to rob them.
The Dominicans are great people and can be very friendly and helpful. But there is a lot of poverty, serious poverty, and rising prices are making life very difficult for many. A single gringo off the beaten path, out of sight of help, will sooner or later during the hike be a temptation that won't be resisted.
Even carrying a gun, which would be illegal in your case, is no guarantee you will be safe because you can't stay awake and alert for danger 24/7.
No, it is not 100% certain that you will be attacked. But the odds are greater that you will be than that you will complete your overnight(s) hike without incident.
If you look fit and confident and are armed in some way, even if only a stout cane that you can use as a walking stick and a means of defense if need be, you can hike during the day with less risk. It is a night, when you can be watched from the brush bordering the coast without knowing you are that you will be at risk