You are correct that DMSA is more commonly used along with ALA in the Cutler protocol, but that is due mostly to better cost and availability. However with people who are very sick and have nasty candida problems, DMPS is almost always preferred if available.
DMPS, like DMSA, will take the HMs out mostly via urine, bypassing your messed up bile flow.
Although I've used DMSA + ALA with good results for my lead problem, I took a close female friend to a doctor who is familiar with Cutler. I knew she was a much better fit for DMPS due to her poor sleep, previous candida outbreaks and sensitive nature. I paid the doctor bill and for the first bottle of DMPS even though I had plenty of DMSA in my refrigerator. After she started getting gains she was happy to pay for additional bottles.
Fortunately we have a few different detox tools in our toolbox. We just need to make informed decisions about what to use and how to use them.