Was Job in the Bible related to Seth?

Yes, through Noah's line. Noah himself was of course descended from Seth. Of course, we cannot really say any more than this, since we do not have any details on Job. But whether some believe Job lived early, around the time of Abraham, or was post-exilic, makes no difference. This is so since all people on the earth are descended from those who came off the ark, and those who came off the ark were Noah and his sons and daughters in law and of course Noah's wife.