Raider's armlets +2 enhance SNEAK ATTACK, not TRICK ATTACK. this is yet another of the countless Typos and mistypes brought to you by the NA translation team.
These do not have any base form of TH+ like Assassin's Armlets do. They increase Sneak Attack damage by a large amount (I assume the same calculation as Rogue's Armlets +1, just with DEX), which leads to higher damage. This leads to the illusion of TH procing more, but Assassin's Armlets still retain their value :]
I might be tripping but..
I can CONFIRM Raider's Armlets +1 has hidden TH trait...
I was doing Ixion mob and Ironclad at vunkler last night with nin, whm x2 thf and on first TH affect hit it was built at 6
I was tp'ing on:
Mandau
Thief's Knife (1)
Raider's Boomerang
Raider's Bonnet +2
Necklace
Brutal Earring
Suppanomimi
Raider's Vest +2
Raider's Armlets +1
Uth Ring
Raja's Ring
Athe Mantle
Twilight Belt
Raider's Cul +2
Raider's Poup +2 (1)
Atma:
VV
RR
SC
Trait: TH3
so if you ask me, the 1 extra TH should come from hands....