Coral chips, coral sand, live rocks .... All these serve the same purpose , surface area for bacteria to grow on,buffer ph and so on ..
If U have coral chips in the sump it increase the overall area where bacteria grow .however coral chips tend to get clogged with detireus and will increase no3 and po4 lvls.
So if u already have enough rocks and sand in the DT u don't need anymore chips in the sump and when u don't have coralchips u don't need to worry about washing them .