A potential player pitched to me the idea of two character concepts: one is to become an arcane archer, the other a dark delver (Paizo splatbooks allowed, no 3PP). He did not expand on what if any game-breaking mechanics he wants to abuse, but I am usually suspect (I used to play and DM in d&d 3e) whenever someone identifies their character progression plans by a prestige class (to the exclusion of other things). Looking at the class features, I don't see too much of issue. The worst I can imagine is the trick from Treantmonk's wizard guide to put Anti-Magic Field on an arrow as an arcane archer. Is there something I'm missing? Throw at me the most absurd abuse of rules that can be accomplished with these prestige classes, please.
You could simply voice your concerns to him in the terms you already listed here...
Just let him know that you reserve the right to veto at a later date if his character becomes unmanageable, I have a player like this and we just sit down and discuss his future character plans from my perspective, rather than strictly rules...
I basically would sit them down and say "okay, how powerful is your character going to get in relation to the rest of the party?"
It's kinda like a contract, or gentleman's agreement... if they violate it, at least you can fall back on the earlier discussion when you nerf them down to match the party again... :D