I did not locate your Joseph Lee Rodman with parents on the 1870 Census. Here is what I did find:
Located Joseph Rodman on page 3 of 5 of 1880 Altus, AR Census, living in a Hammond family household. He is single, age 26. Born MS with both parents born S.C. [On 1920 Census, Joseph Lee indicates one parent born S. C. ] If this is your Joseph Lee, he moved to Altus, AR first, before W. D. Rodman. Heritage of Tate Co indicates Joseph Lee came from N.C. Possibly this should have been S. C.?? This Joseph fits your Joseph Lee in a number of ways.
Joseph Lee married Ollie Garrison 06 Oct 1887, in Tate Co, MS. I didn’t locate any more Rodman marriages in Tate Co during this time period.
I assumed your William Dekalb Rodman is the W. D. Rodman married to Nannie. [I didn’t know how you determined that his middle name was Dekalb.] On 1880 Census, I found W.D. in Marshall Co, MS. On 1900 Census, they are in Altus, AR. On the 1900 Census, W. D. is listed as born Sept 1843 making him too young to be Joseph’s father. Found a 9 year old, William Rodman on the 1850 Northern Division, Marshall Co, MS Census. Could possibly be W. D.?? I believe he was in household of a 50 year old female Rodman, who might be his mother.
Found an Alexander K. and Mary J. Rodman on 1850 Northern Division, Marshall Co, MS Census. On 1860 Census, they have moved back to S. C.; listed in Lancaster, S. C. with three children. They have a son John L., age 9, born MS. Any possibility this John L. could be your Joseph L.?? In 1870 the family, minus Alexander K. is still in Lancaster. John L. is listed as age 19. This is likely a real longshot.
1900 Census lists all children of Joseph Lee as born MS, with exception of Effie, who was born in 1896. She is listed as born in Texas, indicating that they lived in Texas for a a year or so around 1896 to 1897.
I hope this information will be of some help as you continue your search for Joseph Lee’s parents.