If Aokiji agreed with the revolutionaries he would have joined them already. We have no idea what Dragoin's true motives are so I won't accept them as the true bastion for justic. Aokiji is paving his own way for the Marine's path to the lightHe cares about the marines, but he definitely doesn't want Akainu running the show and definitely doesn't like Akainu's ideals. I could see him joining/helping the revolutionaries in order to reinvent the marines more in line with his views. I'd also picture him helping out Dragon's crew over Blackbeard's or any other pirates.