What is Emberpup's traversal ability?

Hustle is an active ability, not a passive one. You turn it on when you want the speed, which makes it something you use deliberately across open ground rather than a background bonus you stop noticing. Emberpup is a traversal pick first.

The name is shared. Helion also has an exploration Mobility ability called Hustle, and on Helion it raises both sprint and movement speed while draining stamina. So the speed on that version is bought with a resource rather than handed to you.

Running Hustle costs you nothing in combat

Exploration and traversal mobility skills are managed separately from your fighting kit. They do not take up active combat party slots or ability slots. Keeping Emberpup around for Hustle therefore does not push a combat option out of your lineup, which is the usual worry with a creature you are carrying for one utility.

What Hustle does not cover

Hustle is ground speed. Other Aniimo handle traversal by opening up terrain instead: gliding, flying, swimming and burrowing all come from different creatures. Celestice, for one, brings level one climbing and flying.

That makes Emberpup a companion for distance rather than access. If a route is blocked by water, a cliff or a gap, faster sprinting will not solve it and you will want a different Aniimo in the slot.

Not settled: Whether Emberpup's Hustle drains stamina the way Helion's version does is not settled. The two share a name, but the exact behaviour on Emberpup has not been pinned down.