Can a wps like markovian advantage activate on the same attack with a devotion proc? Can the third hit of cadence activate devotion procs or %activation on attack skills (not wps but skills that are granted by items)
Yes and yes.
To be more precise, when you activate a WPS that WPS can activate a devotion that’s bound to it, not to the main attack.
For instance, you’re attacking with Fire Strike and have Smite as a WPS. You have Elemental Storm bound to fire strike and Eldritch Fire to Smite. When your attack procs Smite you have a chance to proc Eldritch Fire but not Elemental Storm. If you don’t proc Smite (nor any other WPS) you can then proc Elemental Storm.
Am pretty sure this is wrong. I have multiple ranged characters with 100%wps chances that proc elemental storm and the likes off savagery or firestrike. An alternative possibility is that those procs come from the ongoing damage or secondary effects like bleed damage or brimstone.