If I hold a battlefield playing as akali and I move my only unit back to base from that battlefield can I move my stellacorn horder to that battlefield and activate my akali legend to move it back?

Yes — the whole line works, and Stellacorn Herder draws a card on each leg.

Moving your only unit out makes you lose control of that battlefield (Rule 323.6), but a Standard Move from base to a battlefield doesn't require control of the destination (Rule 144.4). So Stellacorn Herder can still move there — that applies Contested and stages a Non-Combat Showdown, and its "When I move" trigger draws 1.

Once the showdown begins, you're the player who applied Contested, so you have Focus (Rule 345), and Rogue Assassin's Action ability is legally timed during a showdown on your turn (Rule 347.1). Activating it moves Herder back to base — that's a Move, not a Recall, so it draws a second card.

Caveats: the battlefield ends up empty and uncontrolled (no Conquer, since no unit remains when the showdown closes — and you'd already scored it via Hold this turn anyway), and you still can't play units there from hand after losing control; only moves into it are allowed.