Does the paint coat the Styrofoam or dye it? If the paint truly coats it, the PlayDoh will definitely stick if glued to the paint. If the paint only dyes the foam, but leaves the texture as it was, the PlayDoh may or may not stick, depending on the type of glue you use. Check the labeling on your glue. I think Tacky glue (Aleene's) does pretty well with Styrofoam and other foam materials. Check the label, though, just to be sure.
