See Scouting Wolf // Wolf Pack.

Can you explain the timing on this?

Can this trigger abilities of cards looking for creatures entering the battlefield?

It's no different than flip or transform. This doesn't exit and re-enter the battlefield. It simply becomes something else.

Oh wait, you meant this specific card.

Unveil is meant to replace the act of tapping. As this arrives it doesn't become tapped, so you can't replace that. That's the intent, anyway.

Except that the rules (last time I checked) interpret "~ enters the battlefield tapped" as "As ~ enters the battlefield, it does, then becomes tapped" the same way "~ enters the battlefield with a +1/+1 counter on it" becomes "As ~ enters, it enters, then put a +1/+1 counter on it" can be replaced by effects like the one on Conclave Mentor.

That's pretty counterintuitive, if so.

Anything that triggers when a permanent becomes tapped will trigger if it enters tapped, just anything that triggers when you put a counter on a permanent will trigger if it enters with a counter

https://www.mtgsalvation.com/forums/magic-fundamentals/magic-rulings/809590-enters-tapped

The Gatherer ruling on Verity Circle seems to say otherwise.

But then again this isn't a triggered ability.

It's entirely possible the rules have changed since "last time I checked" to account for this interaction, but the fact that it's a question should be kept in mind.

Yes, the confusion here is evident, so it's definitely something to think about.

Clearly this isn't triggered; the part of the ruling that seems relevant to me is that it points out that at no point is the permanent entering tapped untapped. Its existence begins as a tapped permanent, so there's no tapping to replace.