I'm not sure if the Others were ever part of Dharma before, but I certainly don't think they are part of Dharma now...remember that Kelvin called them the "Hostiles" which implies the Others are working against Dharma. For what purpose, who knows...since the Lost Experience revealed that Dharma was working to change the factors of the Valenzetti equation in order to postpone the date that humanity will destroy itself, maybe the Others are working to stop Dharma, which implies they want to hasten the date of humanity's end...just a thought...