The more formidable challenge, particularly in today’s publishing environment, will be to find an agent who can convince the editors and execs at publishing houses that the book will make them money. Publishing is an industry that exists to make money, just like any other industry; the book is merely the product. Authors are in a very difficult position in today’s market, and any work, no matter how meritorious it may be, must convince the publisher that it will be able to sell enough copies to recoup the costs of publishing it, with enough left over to pad the bottom line. Many formerly successful authors are finding it difficult these days to find a publisher, particularly one of the big boys like Random House, Penguin Putnam, Macmillan Publishers, etc. And then there is Amazon, which has thoroughly disrupted the traditional publishing model; more than I want to get into here. Given his subject matter, your friend will likely have better luck with smaller, niche publishers, and may even need to consider self publishing if all else fails.
I wish him luck.