Yes of course it is valid.

Please be aware of the mandatory seat reservations on the Eurocity to Italy + high-speed trains (Frecciarossa or Intercity mainly) inside Italy. These reservations are best bought on the OBB website (Austrian Railways). For all these routes there are reservation-free alternatives which can take a little bit longer (to enter Italy) or quite longer (2 hours more on the RegioExpress between Florence and Rome)

Thanks a lot, Can you please provide the link on OBB website to book with Euro Rail Pass. I have tried but I am seeing only purchase option

You choose a journey, for example Venice to Florence, and add a passenger with a Eurail/Interrail discount (do not choose "seat reservations only"). It should look like this screenshot.

If I remember correctly international Eurocity seats are 11€, Frecciarossa 10€ and Intercitys within Italy 3€.

Let me know if it doesn't work.

Thanks for your time in responding much appreciated will try and keep you posted