Yes the question is: "he says to say or not to say-so"
But that does not necessarily mean the friend does not know. He may just not be advertising it. Which would be understandable.
The question is:
How good of a friend are you?
If you want to address this issue without hurting your friend, irrespective whether he knows or not, what you should do in my opinion is...
Ask the girl whether he knows or not and tell her about your dilemma.
If yes, then you can talk to your friend (if you're ok to tell you punt).
Just make sure he knows you're happy for him if he's happy with her. Also that the word does not get around from you, if that is what he wants.
If not, then ask her what her intentions are:
Is she serious about it? Is she planning on telling and when? Is she planning a career change?
What are her actions after the talk?
Consider also how long have they been together? Is this time enough to make decisions on career change?
Based on her answers you then have to make a decision on whether and when to talk to your friend.
If you want to stay friends... regardless whether you talk to him or not...
don't go banging her... don't try and squeeze her to have sex with you.
There has gotta to be plenty of other girls, so that you don't have to take advantage of the situation.
If he finds out (and believe me he will), he'll never forgive you. Then again... how good friends are you?
That's just my opinion... which often in this world is disregarded.