If Humility is on the battlefield, do creatures that enter with counters from their own ETB effects still get those counters?

Humility gives all creatures base power/toughness 1/1 and causes them to lose all abilities. The critical question is one of timestamp and layer ordering under the Comprehensive Rules layer system (CR 613).

Abilities that place counters on a creature as an enters-the-battlefield (ETB) triggered ability work as follows: the creature enters, then the ETB trigger would go on the stack — but if Humility is already on the battlefield, it has already stripped the creature of all its abilities (in Layer 6, applying before the trigger can be generated in most cases). Because the creature loses the triggered ability before that trigger is ever created, the trigger never goes on the stack and no counters are placed. (CR 603.6d: a trigger only triggers if the object had the ability at the moment the event occurred.)

There is a nuance: static abilities that define how a creature enters (like Stoneforge Mystic's replacement effect, or counters granted by a separate permanent's static ability such as Hardened Scales modifying another effect) are handled differently. But self-ETB triggered abilities on the creature itself — such as Walking Ballista entering with +1/+1 counters via its own printed ability — are lost under Humility.

Concrete example: You control Humility and cast Crystalline Giant. Normally Crystalline Giant enters and its ETB trigger places a random counter on it. Under Humility, Crystalline Giant loses all its abilities upon entering (Layer 6), so the ETB trigger is never generated, and no counter is placed. It simply enters as a 1/1 with no abilities.

Note that if the counters are placed by a replacement effect on a different permanent (e.g., Doubling Season or a card that says 'if a creature would enter under your control with counters...'), those effects still apply because they don't originate from the creature's own ability. (CR 614.1c, 616.1)