Dex is dumb for a tank. Everyone should know it.
The healer will thank you for going full vit.

At lvl 50 you pretty much have all the dex you need without statting it.
You could argue statting STR to reach your next parry and block cap but Vit is still more important as it is not a chance but rather a static gain.

Edit:
But no, never str / dex accs for tank unless you wanna help dps. You will loose parry and other useful stats.