The two questions about the PhD's do feel a little bit misplaced for a startup audience. Who here stops and thinks "Am I supposed to have a PhD to do that?", when setting out to start something new? (<insert theranos reference here>)
PhD is just an academic title and as such it is neither a necessary nor a sufficient prerequisite to approach NLP from a mathematical angle.
The best in what? If you mean pushing the boundaries of research, yes, then your path there will likely involve a PhD. If you mean building the best technology products, then being able to read, understand and implement the biggest recent advances is enough and usually requires far less mathematical knowledge.
(That was intentionally written generically since I think that it applies to more than just NLP)
Yes I mean pushing the boundaries, but I think it is important to stress that a PhD is not a prerequesite to do that. Anyone who is talented enough can learn the necessary math.
Getting paid for research work is a different story of course. A PhD undoubtedly helps with that, but this is Hacker News. People might figure something out.