There's no rule, as far as I am aware (and I've done some officiating) about the sort of pedals you have to use in road racing. However, I'd really advise against it. Having your feet securely attached to the pedals is close to fundamental when you're trying to maximise the power you put out, and I really don't think you'd be entirely safe trying to sprint out of the saddle on platforms in anything other than absolutely perfect conditions.

And it isn't just your safety I'm talking about. If you come off a pedal under hard acceleration you're likely to come down and bring others down with you. Don't do it.

EDIT. In this country, the Chief Commissaire has discretion to prevent anyone racing if he/she considers their equipment unsafe. I'd think seriously about that were I the official. If you've never raced, you may underestimate how intense it is. There is contact between riders, the surges are sudden and fierce, it's pretty full-on. I would not feel safe on platforms myself, so I certainly wouldn't advise a beginner to do it.