So, is this true? Do we have the Gipper to thank for Marilyn?
The story is verified by David Conover’s official website:
And guess who she was? 
However, nowhere in Conover’s account does he say that Reagan sent him to photograph a particular woman.
With pictures of Marilyn in it, I bet the title Yank took on a whole new meaning.

"Ronald Reagan was responsible for the rise of Marilyn Monroe? "
Well, maybe. But if he was normal it’s a good bet that at one time or another Marilyn was responsible for a rise in Ronald Reagan!
Did anyone else read the title as Ronald Reagan being responsible for the rise of Marilyn Manson?
No.
(Raises hand guiltily.)
So it is true and can safely begin spreading the story as fact?
I’d say that it’s mostly not true. Marilyn Monroe was photographed by a man who worked for Ronald Reagan. Reagan didn’t even know of her existence when the photographer took her picture. She might very well have become famous without having been photographed by him.
Yes, it would be equally true to say, “Franklin Delano Rooseveldt is responsible for the discovery of Marilyn Monroe.” After all, he was Reagan’s boss at the time.
It just doesn’t make sense to say “A is responsible for the discovery of B” when A was completely and totally unaware of B’s existence.
Re-read my previous post above: “However, nowhere in Conover’s account does he say that Reagan sent him to photograph a particular woman.”