why is the regime afraid of the OAS inspectors? Also, what other rebel groups were their beside the june 14 movement?

The OAS, otherwise known as the Organization of American States, is investigating the political prisoners' situation in the Dominican Republic under the Trujillo regime. The OAS can help the political prisoners and bring sanctions against Trujillo if problems are found. The OAS did in fact impose sanctions against the regime. 

what other rebel groups were there besides the June 14 movement that the Americans assisted?