Here is from the Accor site, benefits for Platinum members...

Access to Executive lounge
Upon request and subject to availability on arrival at the hotel, if existing (except Sofitel Melbourne, Sofitel Brisbane and Sofitel Sydney).

... so yes you'll get into the lounge as Platinum even if the room you booked does not provide lounge access, but you may need to ask (upon request) and you may be refused entry if the lounge is at capacity (subject to availability). Honestly the latter has never been an issue as far as I'm concerned but I had to "remind" check-in staff in the past.