For your first question of is it possible to make money selling services such as manual directory submissions on DP then the answer is yes. How do I know its possible? For more than a year I sold a variety of different services to the members of DP from things like WordPress customization to link building to data entry. If you have at least one example of your previous work then you should at least get 1-3 buyers per thread your create. That is the reason I was so successful with the DP services.
The second question is how do you find out if the links are do follow.... I am not going to give you the answer to this but give you some advice to search the forum / google and your answer will be found.