The move comes after the resignation of Union of Moderate Party MP, Robin Kapapa.
Our correspondent reported Loughman made the appointment to shore up his numbers amid reports more government MPs could move to the opposition of Ralph Regenvanu.
He says Hymak is believed to be one of those whose loyalty was wavering.
Recently the UMP executive in Kapapa's Tanna constituency called on other party MPs to join the opposition.
With the defection of Kapapa and Christopher Emelee from the government, the Opposition has 24 MPs compared with the government's 28.