Though the unit number is not on the confirmation, it is available online. Go to your II account online and look under your "history" to see the unit that is assigned. That is probably the unit you'll get, though it's not guaranteed.
Royals units are fixed, so owners control their particular units and most will probably use them, therefore they are not under control of the resort to assign to someone else.
The front desk does have some flexibility to swap units that were deposited with Interval International and some company owned units, as well as potentially units that were deposited in other trade or rental pools. Hence it is possible that if there is a problem with a given unit the desk can make a swap. This has been discussed several times on this forum; look over it for the last few months, or search for swap or different unit and see what you find. In my experience we've almost always gotten the unit that was originally assigned, and only got a different one once or twice.
All of the Royal Islander units will have an ocean view, though as you note, you'll see more landscaping from the lowest units. A few that are just above the lobby will have the ocean view partially blocked by the restaurant, but the back of the restaurant is nicely landscaped with plants and a waterfall, so it's still pleasant. IF you are assigned a unit you don't like, you could try begging and pleading for a different one - it might work, and might not.
No matter where you end up - even in the highly unlikely event they put you in the Royal Caribbean or Royal Mayan instead - you'll love being at the Tri-Royals! Don't just stick to the one resort - wander around, try out all the pools and restaurants, and have a great time!
