Should I use Cambden tablets?

Grapes will have natural wild yeast spores on the skins, just waiting to begin fermenting as soon as the grapes are crushed. You will likely have some wild fermentation going on as soon as those frozen grapes warm up close to room temp.

That said, if you pitch a good amount of properly rehydrated commercial wine yeast once you've mixed up your must, chances are that the commercial strain will swamp the activity of any wild strains, and all will be well. However, there is a small, but not totally insignificant, chance that the wild strains will do bad things to the must before the commercial strain comes to dominate. Those bad things could include causing increased volatile acidity (i.e. vinegar), a musty smell/taste, increased H2S production (with that rotten egg smell), etc. SO, many winemakers and meadmakers choose to do a sulphite treatment before pitching the commercial yeast. The choice is up to you.

If you add enough sulphite to knock out most wild yeast strains (around 50 to 75 ppm free SO2), then you can pitch many commercial strains of yeast shortly after the sulphite addition, since many commercial strains have SO2 tolerance levels much higher than their wild cousins. Still, I'm one of those who likes to stress my chosen yeast strain as little as possible, so I'll usually wait 24 hrs or so before pitching my commercial yeast, after a sulphite addition.