Legendary Sting is recommend for the Vulkoor's Chosen set bonus, not the proc which doesn't affect your mainhand.
Wounding/Crit Wounding not works, not so sure about Legendary Virulent Poison. And, of course, this weapon not single mandatory choice for any build.
Offhand procs haven't ever really been a focus for shuriken.
Of course it was really focus for Shuriken. All LGS effect like Affirmation, Ash, Ice etc, Alchemical proc effect (DoT specifically) from Alchemical/Dino weapon always is main focus for off-hand weapon, lol.
Celestia's Greater Sunburst and Echo of Sunsword's Brazing Brilliance can proc using a shuri, but the other effects of those weapons have no bearing on shuri attacks.
Fiery Detonation surely proc too.
Prior to the Vulkoor's Chosen set bonus revamp, it was common to have the old ToEE set bonus for 20 RP with a TOEE kama with armor piercing in the offhand.
It was usual because bugged AA imbues, and, of course, fully stacked +20 Quality MP/RP still very viable... at lvl... and AoE from Epic ToEE martial melee weapon still best damage output from all such AoE sources. 8)
), i always use it on my shury-throwers at lvl7 and until lvl20. At lvl 20 change it to Alchemical crafted ssword/kama with more effects. At lvl26 it is Epic ToEE and LGS. At lvl 30 it's Legendary Alchemical crafted ssword/kama.