you'll find a lot of conflicting nfo on this basically because gourami's are one of those fish that each one will have their own personality and temprement. if the DG's you get are peaceful then no problem they'd be fine with platy's. If you get an agressive DG however then the platy is a similar enough shape and size to be considered a threat and all hell will break loose.
now i wouldn't be too concerned about this though because I would strongly warn you away from dwarf gourami's anyway. There's a specific virus which only DG's get and because of this they're nearly impossible to keep alive. they may be fine for a few months but then they just keel over and there's nothing you can do, i've tried to keepo them several times with no joy and have just given up and I know a significant number of other aquarists who have done the same.
at any rate they are definately not hardy enough for a newly cycled tank.