Hackett, 25, was 8-5-3 with a 2.76 goals-against average in 16 AHL games with Rochester last season, while also making five NHL appearances with Buffalo.
A Calder Cup finalist with Houston in 2011 and an AHL All-Star in 2012, Hackett has made 184 career AHL appearances, posting a record of 86-75-18 with a 2.59 GAA, a .910 save percentage and three shutouts.
Originally selected by Minnesota in the third round of the 2009 NHL Entry Draft, Hackett has a record of 4-17-2 (3.11, .906) in 26 career NHL games.
Mueller, 29, recorded 14 goals and 26 assists for 40 points in 64 regular-season games with Hartford (AHL) last season, then added five goals and four assists in 15 postseason contests. Mueller also picked up one goal and one assist in seven NHL games with the New York Rangers.
In 447 career AHL games, Mueller has registered 131 goals and 155 assists for 286 points. He was an AHL All-Star in 2012, and won the Calder Cup with Texas in 2014.
Piskula, 30, appeared in 67 AHL games with Milwaukee last season, notching one goal, 16 assists and a plus-20 rating. He also skated in one NHL game with Nashville.
For his career, Piskula has recorded 13 goals and 102 assists for 115 points, along with a plus-78 rating, in 533 AHL games with Milwaukee, Abbotsford and Manchester. He has also appeared in 13 NHL games with Nashville, Calgary and Los Angeles.