Can minnows live with platies

If by "Minnow" you mean White Cloud Mountain Minnow (Tanichthys albonubes) yes they can be kept with Platties. If on the other hand you are refering to some wild fish called minnows locally, in a creek or stream, then it would depend upon the locality of the stream/creek and what it's ambient temperature is. If the water is often below 65F then the wild fish would not live in the tropical temperatures required for Platties healthy.