The Washington Free Beacon hired Fusion GPS. The DNC took over the research after Drumpf became the face of the Republican Party (and why not?), during which time Steele discovered unusual and shocking evidence of Russia contacts with one of the two candidates (the one NOT named Clinton). Steele took notes. Notes are not a report. Notes are notes...I assume there would be some confidence in some of the notes, and some we-don't-have-solid-proof-so-don't-use-this-without-verifying-it on others. Buzzfeed published them anyway.
Now, Buzzfeed is being sued for libel because they published the unverified memos, nobody asked them to...they were notes, not press releases...the dossier has some things that were verified, and some that were not. The DNC did not publish the notes, so they are not being sued for libel, Buzzfeed is.
The DNC may not have, or maybe they do have, corroborating evidence of the notes - but I imagine that they don't have evidence that ALL of the notes were verifiable. If someone was going on a fishing expedition to see which parts of leaked notes were corroborated by the DNC (if any), why would the DNC play ball? Someone asking you to open your servers because they published some notes by a person who was doing research for you seems a bit sketchy.
How this implicates the DNC of any wrongdoing is beyond me. The ratf'ers in the Republican Party are fishing and spinning to make this about the DNC. If anyone should open up their servers for an investigation, it's the RNC.