Not true. When I killed a thief that tried to rob me the US Consulate came to the Police station. It was Bill Kirkman at the time. He was a non factor anyway. I did fine on my own. But he was there even though I am a dual citizen.
Maybe it is different for US,DR dual nationality but it is certainly true for UK.DR nationality. Herewith quote from UK Foreign Office publication.
Dual nationals
If you are a dual British national in a third country (that is, a country of which you are not a national) and hold a valid British passport, we will offer you our full support.
If you are a dual British national in the country of your other nationality (for example, a dual US-British national in the US), we would not normally offer you support or get involved in dealings between you and the authorities of that state. We may make an exception to this rule if, having looked at the circumstances of the case, we conisder that there is a special humanitarian reason to do so.
Maybe worth checking depending on nationality.
Matilda