It's possible Shae is an ancestor to Tor and Pre Vizsla. Last names change over the years due to mispronunciations and misspellings and etc. Example: My friend's last name is Glasper, but originally it was spelled and pronounced Glasner in German. Considering SWTOR takes place hundreds of years before Tor and Pre Vizsla show up it's possible the name went under some changes. Or it could be Bioware just gave her the name Vizla just because it sounded like a cool name. Or they could have purposely left out the "S" to deter any relations with the Death Watch Leaders.
Honestly....I wish Shae had a role in the game instead of just showing up in the trailers...would have loved to meet her. Wait...do you guys know if you can find her in game because if so please tell me.
There's a Vizla in TOR, but not Shae. Only Gen Vizla, one of the trainer duos that help you decide your AC. Hopefully Shae will show up in ROTHC.
And yeah, I believe it's the same clan. Mandos don't write everything down, they pass their stories down orally, so a lot of things can change down the line. Or it could be a separate clan that traces it's history back to the same source. We have the Antilles house of Alderaan and the Antilles family of Corellia, after all. Same name, different houses.