You will never know the whole story. Yes, he may have had a good paying job, but maybe the divorce or not being with the children and their mother (if not married) left him in a ton of debt. Or maybe he was horribly depressed and he spent money recklessly or maybe he just didn't care at that point...who knows?
If you're friend has a job (which I assume she does) then my advice would just to keep her finances completely separate from him. (which is usually a good idea unless you are married anyway.) If she wants to date him, she is going to and really nothing you say is going to sway her too much. You do run the risk of having your friend think you are not respecting her decisions or her judgment and that could cause resentment in the friendship. Is it worth it? He's not violent. He's not a wife beater, a rapist or a child molester. In those cases I am all for intervening. With this, maybe he is just one of those men that take a really long time to grow up and become responsible. Some men have a really hard time putting anyone else's needs before their own. I think it is horrible when men (and women) don't support their children, but again, its not what I or you think that matters right now, its what your friend thinks that counts.
My own Da will tell you, it wasn't until he was in his mid 30's that he was anywhere near responsible enough to be a husband and a father. That would be fine if he wasn't married and with 2 (soon to be 4 kids) in his mid 20's. However, my father is a very good man, a good father and good husband.
Give the guy a chance. If your friend likes him, let her explore the relationship. Maybe nothing will come of it, maybe they will fall madly in love. Who knows?
I understand you are only looking out for your friend, that's what a good friend does. Hopefully your friend will be going in to this possible relationship with her eyes wide open.