Darje asked for Rado, they shared an agent so no doubt they knew each other even if it wasn't professional. It looked like a great signing, someone with a lot of A-League experience and player contacts who could help Darje adjust to the league and augment where he lacked.
Hindsight is always 20/20 but if you wanted to get an assistant which provided some of the knowledge that Darje was lacking then I can't think of too many better options, that must have been in Darjes mind when he asked for him.