if shuriken flip kills the last enemy unit, can a hidden card be played against the unit moving into the bf

No. After Shuriken Flip resolves, the cleanup removes the hidden card before you ever get a window to play it.

Here's why: you can't react during Shuriken Flip's resolution (no cleanup and no reaction window while a chain item resolves — Rule 321). Once it finishes, a cleanup runs in this order: you lose control of the battlefield (your last unit died, so no units remain — Rule 323.6), then any hidden cards there are sent to the trash (Rule 323.7), and only then is a Showdown staged (Rule 323.8). The hidden card is gone before the Showdown exists, so it can't target the unit that moved in.

One exception: if another trigger goes on the chain (e.g., the moved unit has a "when I move" trigger), the game is in a Closed State, control isn't lost, and the hidden card can be played as a reaction to that trigger before cleanup. (FAQ #11647)