I was researching the Simpson/Stephenson connection yesterday and YES...in MY opinion...I think this IS the likely connection, but I do NOT have the complete documentation to back it up yet.
My grandmother was a Simpson. She's alive and well and will be 103 in October 2014, with her intellect completely intact! She always knew growing up that there was a Simpson/Stephenson connection in the Laurens area of SC...so that really increases the odds we are right in my opinion. She didn't know there was a marriage, but the family story through her father was one of her Simpson ancestors was a "stock man" for the Stephenson family in the 1800's. Definitely worth checking further!
Dawn Warner Perry