I didn't find a DAR record for him, but his son-in-law has one: Elias Roberts, Patriot Ancestor #A096858.
No James/Jacques Roux (or "sounds like Roux") pension application transcribed & posted by Southern Campaigns Revolutionary War Pension Statements & Rosters (none for Elias either).
take a look at:
"États Unis, Combattants français dans la guerre révolutionnaire, 1778-1783," database, FamilySearch (https://familysearch.org/ark:/61903/3:1:3Q9M-C9BF-17DD-M?cc=2758243 : 14 August 2019), > image 1 of 1; records compiled by France. Ministère des Affaires Etrangères. Filmed by the Genealogical Society of Utah, 1968. Citing United States. French Combatants in the Revolutionary War, 1778-1783. Washington, D.C. : 1905.
by share coincidence I found Jean Roux Quarter Master:Image 300
https://www.familysearch.org/ark:/61903/3:1:3Q9M-C9BF-17DD-M?i=299&cc=2758243&cat=2700559
There are multiple men named Roux so I would not assume that Jean is your James (according to translator James is French for James)
Index image 513 page 443 contains 2 columns of men name Roux, lots of Jeans.