I don't think how often the joint is recruited is as important as how many total joints. That's always been my understanding of it, anyway.
I don't know if an SLDL or an RDL are varations of eachother or not...I don't know which came first. You could say that an SLDL is the straight leg variation of an RDL, or that an RDL is a bent variation of an SLDL. Kind of a chicken and egg logic, I suppose. Neither one are a "dead lift," and that's the only point I'm making.
As long as your variation works for you, and you are performing it safely, I don't suppose it matters much.