Answering my own post with updates from discussions with our BnB owner.
Here is the list of guaranteed Intercity and Frecciarossa fast trains:
https://www.trenitalia.com/content/dam/tcom/allegati/trenitalia_2014/informazioni/TABELLA_A_Treni_garantiti_DPLH.pdf
And here is a list of the Regionale trains for the Veneto that are guaranteed:
https://www.trenitalia.com/content/dam/tcom/allegati/trenitalia_2014/in_regione/treni-garantiti/Regionale%20Veneto_sito.pdf
If I'm reading this right it looks like 9753 Verona 19:30 - Venice 20:42 is guaranteed. It wouldn't be my choice but it would be okay. Or the 9755 at 20:00 is guaranteed as far as Mestre at least (it goes on to Udine).
Earlier it looks like there's only the 9715 Verona 10:30 - Venice 11:42 in the morning.
i'm considering buying a super cheap italotreno ticket for 18:49 > 19:50 into Venice and if it doesn't go just wait for the Trenitalia at 19:30. If I buy a Base price Trenitalia ticket I'll have to wrestle them for a refund but it could technically happen.
Or maybe do the opposite and book the Frecciarossa train at 10:30 and then the italotreno at 10:49 as a back-up option. I know i'm probably throwing some money away to have the insurance of back-up plan but if it works I think it would be worth it for the really cheap tickets.
Keep in mind if this happens as a general strike buses and other transport to and from stations could be affected.
We'll see how it all goes,
=Tod