Curing salt has nitrate / nitrite in it, which is to prevent botulism. You shouldn't need it for gammon, though, I take it you'll be cooking it anyway and your kitchen is clean?
You'll see nitrate and nitrite mentioned in books a lot as the writer wants to protect himself from any claims, but the chance of botulism in really really tiny (but it's potentially fatal). Google botulism and you can then make up your mind. We don't use it, but some wouldn't dare not to.
Enjoy the gammon!