I am contemplating whether the use of research questions is enough in writing a dissertation on implementaton of educational policies in Some states in Nigeria
For an hypothesis to be used in a study, there should be availability of at least two variables. That is one dependent and one independent; the hypotheses would then show if one hypothesis would have influence on the other. You may need to shed more light on your title so as to give us more understanding of the scope.
From your topic I can infer that you most probably intend to conduct a qualitative analysis on implementation, like discourse analysis, for instance. Therefore, since you are probable not meassuring it in a quantitative way) there is no need for a hipotesis, understood as a statistical one for a quantitative design. Look for policy analysis and qualitative research designs.
Whether you use hypotheses or research questions depends on the kind of study you want to do. Studies which evaluate implementation of educational policies usually tend to be qualitative in nature, requiring an open ended exploratory approach to understanding whether or not implementation has been successful. If your research questions are well constructed, then these should suffice for your study.