Associated Press have picked up on the 'no warning' issue - see Sun Sentinel:
'People complained on local radio that they were not warned of the water release from the dam, and officials acknowledged it might have caused some of the deaths..............As heavy rains began to overwhelm the Tavera Dam, outside Santiago, the country's second-largest city, officials gave the order to begin releasing millions of gallons per second into the river, said Ismael Matias, planning chief of the Dominican emergency operations center.
Local authorities had warned repeatedly that a release was possible during the storm and told people to evacuate areas in the path of floodwaters rising as high as 66 feet above normal, Matias said. It was unclear if the warnings were heeded or even relayed.'
Olga kills 8 in Puerto Rico, Dominican Republic -- South Florida Sun-Sentinel.com
And looks like President hasn't gone to Santiago
La República - Presidente Fernández amaneció anoche en Palacio recibiendo informes de las provincias
Video of tree clearing & flooding in Montellano
YouTube - EL DIA DESPUES - tras el paso de la Tormenta OLGA