Although a creature put onto the battlefield this way is attacking, it was never declared as an attacking creature. Abilities that trigger whenever a creature attacks won't trigger when that creature enters attacking.

You choose the player, planeswalker, or battle each token is attacking. Each token can enter attacking a different player, planeswalker, or battle. They don't need to be the same player, planeswalker, or battle that the creature returned to pay The Last Ronin's Technique's sneak cost was attacking.

If a creature spell's sneak cost was paid, the creature it becomes enters tapped and attacking the same player, planeswalker, or battle as the creature that was returned to its owner's hand to pay its sneak cost. This is a rule specific to sneak; in other cases, when a creature is put onto the battlefield attacking, that creature's controller chooses which player, planeswalker, or battle it's attacking.

Spells can only be cast for their sneak costs any time you could play an instant during the declare blockers step on your turn (after your opponent has decided whether to block).

Although the tokens enter attacking if The Last Ronin's Technique's sneak cost was paid, those tokens were never declared as attacking creatures. Abilities that trigger whenever a creature attacks won't trigger when those tokens enter attacking.