Some results:
As Gorn attacking a Klingon/Korgath hex (enemy to Klingon, friendly to Korgath, which Klingons are also friendly with), I was able to hurt the Klingon DV -- in other words, no cartel interference, at least as long as there weren't any Korgath in the mission (I'm guessing that would mess things up).
As Klingons, Tempest and I were able to boost that Klingon hex after first weakening it by 2 DV as Gorn/Fed (one mission me solo, one both of us). With 2 missions, we boosted the hex from 3 to full-health at 5.
Next up, we tried PvP in a Klingon/neutral hex as Klingon vs. Fed. I attacked Tempest's Fed fleet with, I think, a Met_NW10Patrol. The mission spawned Romulan allies for me (2) and 2 Fed DDGs to back up Tempest's CVB and CC+. Oddly, just as I was about to die a nice, painful, Klingon-like death (the Roms were already gone), the mission said "Closing Session" and quit. As I tried to get out of debriefing, I lost connection to the server, so I don't know where the problem was. Either the mission ended prematurely (once the Roms were done?) or the server crash affected it. I doubt it was lag causing me to seem OK when Tempest saw me as dead, because I did not see any lag up to that point. I haven't yet heard Tempest's side of the story.
So far, I'm encouraged by the DV changes. I'm seeing boosts when they should happen with most missions, and DVs going down when they should. The only major problem seems to be neutral coop with same-race players, but we can do without it considering allied coop seems to work.