Etrata, the Silencer and token creatures
Yes, but it doesn't count towards losing the game because it's not a card.

If Etrata’s ability exiles a token creature, it won’t count to determine whether three cards are exiled with hit counters.


Creature tokens on the battlefield are creatures, so they are valid targets for Etrata's ability.
When Etrata's ability resolves, the following happens:

The targeted token is exiled.

A hit counter is put on the now-exiled token.

Token aren't cards,[CR 108.2] so you don't lose the game.

Etrata is shuffled into its owner's library.


Immediately after Etrata's ability resolves, the following happens:

Tokens outside of the battelfield cease to exist as a State-Based Action.[CR 704.5d]



108.2. When a rule or text on a card refers to a “card,” it means only a Magic card or an object represented by a Magic card.
108.2b Tokens aren’t considered cards—even a card-sized game supplement that represents a token isn’t considered a card for rules purposes.
704.3. Whenever a player would get priority (see rule 117, “Timing and Priority”), the game checks for any of the listed conditions for state-based actions, then performs all applicable state-based actions simultaneously as a single event. [...]
704.5. The state-based actions are as follows:
704.5d If a token is in a zone other than the battlefield, it ceases to exist.