Achdus with reshaim is forbidden and is damaging to the soul. Darkei Shalom is very different than achdus; darkei Shalom could be used by gentiles, too, with whom there also is obviously no achdus.
Regarding reshaim, Dovid HaMelech wrote in Tehillim: “Halo misanecha Hashem esna…”
Real achdus is among G-d-fearing Jews, not reshaim who are, at most, irrelevant.