I don't think it's within my power or anyone else's to turn many people into a success if they can't grok pointers, recursion and/or abstraction and one or more of those is necessary for the job (I'm assuming a small enough startup they can't be put someplace "safe").

I'm pretty sure the abstraction bit is innate (I'm assuming they've passed high school math), and very sure I can't teach it nor is it my duty to. Pointers and recursion are not so bad (but again, in these sorts of situations I'm probably not in a position to get them up to speed on something so basic and so far reaching in effects (especially unsafe pointers)).