All DJ ground staff, apart from those in SYD domestic, ADL, MEL domestic and BNE work for contract companies - which at the majority of ports is Aerocare.
I'm not really sure how the operation in PER is run, nor do i know whom Skysatr are. Another contractor i guess.
I know there is quite a large contingent of Aerocare staff whom work as relief crew. Thy are trained using the same facilities and syllabus as every other DJ crew - probably by DJ's trainers as well i would imagine. Talking to some of the aerocare cabin crews, the very rarely have to fill in for those who have gone sick etc. They do fly at least once every month to remain current though.
Skysista - i don't know that i am 'happy' about the whole split thing - i guess you just deal with it after a while. Most of the ground crew at Pac Blue in Syd get on pretty well and always find some way to fill in the time. I can tell you the split shifts don't do much for retention rates though.