No.
His father's prior marriage would not affect the question of whether the father and mother were in "wedlock" for purposes of Sec. 1409(c). If the Stanley Ann/Obama Sr. marriage were contracted in the US, it would be voidable; and it would have constituted the crime of bigamy. But as between the parties and those whose rights were affected by validity (children), the marriage would be treated as effective until terminated by a court. The actual extent of the rights of the parties might differ state to state but as to the federal citizenship wedlock issue, the courts would hold they were married.
Further, if they were married in Kenya, the marriage would presumably be valid under local law and there would be no doubt it was an effective marriage for purposes of the wedlock issue. The first wife might be grounds for divorce in the US but that wouldn't affect validity of the marriage.
I wanted to post those links because there is lots of authoritative information about all of these topics there.