If I guy had kids when he was 30 and remarries at 50, is he just as likely to give her a healthy baby?

Yes! :-) Men can father healthy children at any age, and a father's age has no effect on pregnancy or the health of the baby. (however, those middle-of-the-night diaper changes and feedings do take more of a toll on older parents, compared to when we were in our 20s and full of energy...) congratulations and have fun!