DD was on her back for the first week (ventilated for 4 days), by the time they'd turned her over her back was dry and peeling from being her her back. They had to rub olive oil on her. It was gross.
BAL, Hannah was turned all the time and she had a weird shaped head for months, we ended up having to use special pillows to try and get her head round rather than flat on both sides.
DD slept on her tummy in RCH, but when she was moved to Bendigo she wasn't monitored so she wasn't allowed to sleep on her tummy anymore.
She's about to turn 1 and she's only just started sleeping on her tummy (mainly because we can't keep her tucked in).

It's a good question and I had to ask when DD was in RCH.