10 years before the Battle of Marineford, Dragon had ordered his men to locate the sole surviving Archaeologist of Ohara, Nico Robin who became known as the “Light of the Revolution” among the Revolutionaries.
Though his exact reasons for doing so remain unknown, it is known that he wanted to meet Robin for a long time (even before she became a member of his son’s crew). The first members of the Revolutionary Army that Robin met (to her knowledge) were the ones liberating the slaves at Tequila Wolf.
She was surprised to learn that she was referred to as the “Light of the Revolution” by them and that they had been searching for her for 10 years under the orders of none other than Dragon himself. After the Revolutionaries liberated Nico Robin from Tequila Wolf after she was sent there by Kuma, Robin decided to meet with Dragon after receiving Luffy’s message to wait 2 years in the newspaper. During those 2 years, Nico Robin became acquainted with Dragon and the other Revolutionaries like Sabo and Koala.
During the Zou Arc, Dragon asks Koala about Robin as he and the other Revolutionary’s were worried due to rumors that Robin had been captured on Sabaody Archipelago and was relieved to hear the rumors where false, showing that Dragon at least cares about Robin’s well-being.
Given all the strong friendships/family ties between the Straw Hat Pirates and the Revolutionary Army (Luffy with Dragon and Sabo, Koala with Jinbe and Robin, Ivankov and Inazuma with Luffy and Sanji), we can expect that the Straw Hat Pirates will join Dragon’s Army in the final war against the World Government after Luffy has become the King of the Pirates.