Uncanny dodge=No surprise?

[DarkEternal]

One of my players is playing a Stalker, and he's got Uncanny Dodge as a class feature. They were surprised by drow rogues and since the Stalker was the first in line, the drows fired off poisoned crossbow bolts into him. Since he's a Stalker, he has some nifty maneuvers, like the one for teleporting as an immediate action and so forth. Now, the rules say that you can't use immediate actions if you are surprised in battle or caught flatfooted. Uncanny Dodge says you can't be caught flatfooted. So by that logic he should have been able to use maneuvers before his first turn, right?

[Deophaun]

Nope. The rules say that if you are unaware, you do not get to act in a surprise round. The flat-footed condition is a consequence of not being allowed to act, not the cause.

[Firest Kathon]

Immediate Actions (http://www.d20pfsrd.com/gamemastering/combat#TOC-Immediate-Actions):

You also cannot use an immediate action if you are flat-footed.
Uncanny Dodge (http://www.d20pfsrd.com/classes/core-classes/rogue#TOC-Uncanny-Dodge-Ex-):

She cannot be caught flat-footed,
So the Stalker is never flat-footed, meaning they can always use their immediate actions even in the surprise round or before their first turn in combat.

[Chronos]

Note that there are at least two slightly different versions of uncanny dodge, which interact with flat-footedness in different ways. Check the exact wording of the Stalker's version.

[Strigon]

...They were surprised by drow rogues... you can't use immediate actions if you are surprised in battle or caught flatfooted... you can't be caught flatfooted. So by that logic he should have been able to use maneuvers before his first turn, right?

I think you've answered your own question.
Unless it specifically says he can't be surprised, he can.

When you're surprised, you're also flat-footed. Removing the latter does nothing to the former.

[Psyren]

As written, being surprised keeps you from acting whether you're flat-footed or not. However, Uncanny Dodge does allow you to keep your Dex and Dodge bonuses while surprised, so the Stalker might not have gotten hit by the Drow even if he couldn't blink out of the way.

[Sacrieur]

You can't act in the surprise round if you're unaware of your opponents at the beginning of the surprise round.

[Deophaun]

So the Stalker is never flat-footed, meaning they can always use their immediate actions even in the surprise round or before their first turn in combat.
That's not the relevant portion of the PFSRD. This is:

Combatants who are unaware at the start of battle don't get to act in the surprise round. Unaware combatants are flat-footed because they have not acted yet, so they lose any Dexterity bonus to AC.
You do not get to act. Then, because you do not get to act, you are also flat-footed. Uncanny dodge prevents the later, but does nothing against the former.