Does Vedalken Orrery allow you to cast creatures with enter-the-battlefield triggers at instant speed during combat?

Vedalken Orrery states that you may cast spells as though they had flash. Flash (CR 702.8) allows a spell to be cast at any time you could cast an instant — including during combat, on your opponent's turn, or in response to another spell or ability.

Casting a creature spell during combat (e.g., during the Declare Blockers step or the Combat Damage step) is perfectly legal as long as a player has priority (CR 116.1). After blockers are declared, each player receives priority in turn before combat damage is assigned, giving you a window to cast spells.

When the creature resolves and enters the battlefield, any enter-the-battlefield (ETB) triggered abilities trigger normally (CR 603.2). Vedalken Orrery has no effect on the trigger itself — it only enables the casting timing. The ETB trigger goes on the stack and resolves as usual.

Concrete example: Your opponent attacks with a 5/5. During the Declare Blockers step, after blockers are declared, you cast Mulldrifter (normally a sorcery-speed creature) thanks to Vedalken Orrery. Mulldrifter resolves, its ETB trigger goes on the stack, you draw two cards, and then you may declare Mulldrifter as a blocker — wait, blocking has already been declared, so it cannot block this combat. However, it enters and you still draw two cards.

Note: while Vedalken Orrery lets you cast the creature during combat, it cannot retroactively allow the creature to block if blockers have already been declared (CR 509.1). Timing your cast matters for what the creature can do once it arrives.