Not that anyone of us (or possibly even bungie themselves) really know, but I immediately disregard any lore theory that the speaker is secretly (insert crazy idea/character here). The whole speaker is evil, or is Taox, or is somehow a puppet of Savathun or one of the nine, etc were all theories floating around. Other than the speaker being so vague and undeveloped as a character that he could literally be anyone or anything (I mean, have you ever actually seen sweeper bot and the speaker in the same room??!?!) there is no proof or even hint that he is related at all to anything cabal or anything else.