Kirk Muller was not successful with the Carolina Hurricanes. He was also not unsuccessful. He was a .500 coach with a team that, admittedly, hasn't had much of an identity since their 2006 Stanley Cup win. After a 7th place finish in the Metropolitan Division, the Canes let him go as part of the managerial and coaching re-build under Ron Francis.
The Blues, who did not renew the contract of Gary Agnew, brought Muller aboard as an assistant coach for the Blues because of his successes as an assistant coach, not head. He's been a successful assistant with the Montreal Canadiens as well as Team Canada. He also helped the Habs win the Stanley Cup back in 1993, so he has a Cup-winning pedigree as a player, which is something perhaps that he can pass on to the team.
He also played for Hitchcock in Dallas for three seasons.
Shocking, I know. A Dallas connection? No! If this Dallas Connection can fix the abysmally predictable power play, then more power to him.