Yes, I would look for him, (but would not contact him), the blame is mostly on the grandparents. It's ultimately your husbands decision if he wants to know your findings and initiate contact, but this man has a posterity too that deserve to know who this person is and it would be good to know if he has any health issues that your husband and children should be aware of. I know you can find people using their ss#, plenty of 'people finder' websites, but hard to tell which are scams or not.
this may be helpful, it is from a genuine genealogy researcher:
http://www.ehow.com/video_###-###-####_find-someone-socia...
video transcript:
"Hi, I'm Richard Goms from Salt Lake City, Utah. We're talking now about how to find a person using their Social Security number. There are a number of reasons why you might want to do this. You might have lost track of a family member, you have their Social Security number, you want to track them down. You may have a list of children that you have a list of Social Security numbers for, but you don't know which one belongs to which. Or you may be an employer, ready to hire a person, you want to verify their Social Security number. In order to look up a person who is living by Social Security number, there are a number of websites that will allow you to do this. Most of them charge a fee. However, the United States Social Security website will allow you to look up ten numbers per day as a free service to American citizens. It's a little easier to look up an individual who is deceased. There is a Social Security death index that is available online on many different websites. Familysearch.org is one. Rootsweb is another one. And, you can look up the individual by Social Security number that way. You can then, if you'd like, to get more information you can order the Social Security application from the Social Security Department.