From the descriptions of Arakkoa archaeology items, it seems the Outcasts worship the Old God seen in Outland, and it seems that Old God is under Skettis. Not only that, but the uncorrupted Arakkoa seem to be afraid of "catching" the curse the deformed Arakkoa have. From the Archaeology item called "Outcast Dreamcatcher" the curse is called the Curse of Sethe ("Sethe" possibly being the name of the Old God?). Terokk also seems to have been cursed and exiled, despite being the champion of the Arakkoa god, Rukhmar. In the current timeline, worship of Rukhmar was abandoned in favor of worshiping the Old God. Rukhmar is also called the "Sun-God" here, and Terokk apparently was once the king of the Arakkoa.
Talonpriests are part of the Outcast culture, and they seem to worship Anzu, as well.
The Apexis have apparently been long gone by the time we go to Draenor.
Dreamcatcher - When Terokk returned from exile he was broken and flightless. Rumors of his cursed state swept like wildfire through the Arakkoa, giving rise to superstitious charms and cures. Dreamcatchers endure as one of the most clung-to icons of safety, for the Arakkoa believe the curse will entangle itself in the dreamcatcher and fade in the morning sunlight.Burial Urn - In death all Arakkoa seek to join the Sun-God Rukhmar in the skies above Draenor, thus cremation is vastly preferred to burial. Some have their ashes scattered high in the skies, others are collected in ornate urns and placed in crypts.Decree Scrolls - The incomplete writings here seem to indicate a decree of a sort of martial law, and reminders to be vigilant for signs of the curse amongst neighbors and friends.Solar Orb PH - Central to High Arakkoan culture is reverence of Rukhmar and the sun. Hundreds of Solar Orbs are scattered around [Explosion Town], which cast a never-ending light so no Arakkoan need go without the sun's warmth, even on a cold and overcast day.Sundial - This delicately-engraved instrument, when positioned correctly, acts as both a sundial and an arakkoa seasonal calendar. The base of the instrument is covered with callouts for celestial events, most of which are accompanied by grave warnings. Interestingly, the device seems to have cryptically predicted the arrival of the draenei a century before it happened.Talonpriest Mask - Believing they have been abandoned by the sun, cursed Arakkoa prefer to hide in the forests or beneath awnings during daylight hours. Talonpriests take this a step further and never show their faces to the sun, wearing ritual masks that act as a focus for their communes with Anzu.Outcast Dreamcatcher - Outcast Arakkoa have repurposed the dreamcatcher not to ward off the Curse of Sethe, but to capture and harvest tiny amounts of essences from their lost gods. Rumors persist of an ever-growing mass of swirling energy buried deep beneath Skettis, whispering promises of power to any who will listen...Apexis Crystal - Scattered in the most ancient of ruins on Draenor are fragments and whispers of the Apexis civilization, who attained a height of power during the Age of Order and then abruptly vanished. The arrival of the Iron Horde has prompted a secret but urgent escalation in retriving Apexis artifacts by the Adherents.Apexis Hieroglyph - Brittle and ancient beyond measure, this stone tablet contains carvings that vaguely describe an engine of incredible power, claiming to harness the power of the sun.Apexis Scroll - This battered scroll case has corroded shut, and the scroll within is barely readable with very careful examination. These appear to be plans and measurements for a glorious Temple in the Sky written in an ancient hand. It's unclear whether such a splendid structure was ever built.Beakbreaker of Terokk - Eschewing traditional Arakkoan weaponry, Terokk carried this cudgel as a symbol of his fall from king to outcast heretic. Rumors have persisted for centuries that rather than employing traditional wing-cutting as a punishment, Terokk simply shattered the beaks of those who dared to oppose him.