I have read Winnicott. What he talks about has nothing to do with what OP described. Winnicott talks about evoking the long time forgotten ability to play in the patient, and by "play" he means literally the process of playing imaginative games that allow to express child's creativity. This has nothing to do with the flirtatious playfulness between T and client, the one the OP's T seems to exhibit. I never read anything about this particular behavior in Winnicott's writings and I highly doubt he would endorse it.