The duo have made five appearances for the Robins so far, with Hallam scoring in his last two games, against Bromsgrove and Needham Market respectively.
Attacker Hallam (24) has made a total of 33 appearances in all competitions for the Iron since signing in January 2019, scoring three goals, and has recently made a return from long-term injury.
Left-back O'Malley (21) has played 79 times for United, including 20 times in the National League this season.
