Caddis skippered the Robins to the League Two title last year but has not featured at all this term after falling out of favour with manager Paolo Di Canio.
He was stripped of the Swindon captaincy just over two weeks ago after Di Canio questioned a change in attitude from the 24-year-old.
The former Celtic defender, who only penned a new contract with the League One club earlier this summer, could now make his debut for Blues in Saturday's home clash against Peterborough.
Meanwhile, Rooney could also make his bow for his new club at Preston on Sunday having moved to the County Ground until the end of the campaign, with a view to a permanent switch.
The 24-year-old signed for Blues from Inverness last summer and managed seven goals in 27 appearances in his first season at St Andrew's, although he has been restricted to just one substitute display under Lee Clark.