Can you hide a card from Reksai trigger?

No, you cannot hide a card using the ability of the Rek'Sai legend (Void Burrower).

According to the RiftJudge FAQ #9225:

1. Hiding is a Discretionary Action: Rule 408.2 states that "Hiding is a Discretionary Action." Rule 408.2.a specifies that the Hidden keyword allows a player to pay a cost to hide a card "any time they have a Hidden card in their hand or Champion Zone and meet the prerequisites."
2. Hiding vs. Playing: Hiding a card is distinct from playing a card. As noted in FAQ #7169 and FAQ #5902, hiding is not the same as playing a card.
3. Ability Restrictions: The ability on Void Burrower instructs you to "play" a card. It does not grant you the ability to perform the "Hide" action. Because the card is being played from the top of your Main Deck (a zone that is not your hand or Champion Zone), you do not meet the prerequisites to use the "Hide" action defined in Rule 737.1.b.

In summary, because the ability specifically instructs you to "play" the card, and hiding is a separate discretionary action with its own specific requirements (hand/Champion Zone, paying the hide cost), you cannot use this ability to hide a card.