The information found above regarding JOP Hargus first wife tends to confirm my suspicion. I believe that Milton was the son of Nancy Myers, but not necessarily the son of J.O.P. Hargus. Milton was born in November 1851 and JOP's first wife died in May 1851.
I was also surprised that JOP had other children living with him in 1860 and 1870, the oldest John born about 1859. But Milton was not with the family.
I believe I located Milton here in Bates Co. MO 1860.http://interactive.ancestry.com/7667/4233391_00204/40057749?...
Note that there were boys Fredrick 20 and Wilson 17 in the household.
I located the same family in Sumner Co. TN in 1850.http://interactive.ancestry.com/8054/4206054_00433/6938428?b...
Unfortunately, the previous page showing parents was apparently not filmed. However, note that there is a dau Nancy, age 20.
Sumner Co. just across the border from Simpson Co. KY.
I have not yet found Milton in 1870.
Have you gotten a copy of Nancy Hargus's confederate pension file? It should include info on where and when they married.