The last time I was there, there was a Platinum check-in line near the far left of the the multiple check-in lines in the lobby. It was not a separate room like there is for 7* and Diamond, but it was a separate line.
I check in at the Diamond room, but if you staying at the Augustus or Octavius rooms go to the chck in by Starbucks, near Diamond lounge. Also the waits are not bad at all at regular check-in, nothing like Flamingo!!!!