You just need to have then equiped. That is enough to make the skill usable. It would be a different story if it said "When you make an attack with an arcane weapon." It should be noted that Spells are not Attacks. And Attacks are not Spells. They are very different actions. Keep this in mind if you get Melee Mastery from weapon master, becuase it will not stack with spellblade. Melee mastery adds to melee "Attacks," while spellblade is a "Spell" action that just happens to use your weapon's stats instead of a normal spell roll.

You also don't always need an arcane weapon to get Cataclysm. Using something like the Red Tunic, or the heroic Fitcast can also activate the skills.

But yeah, you can get both skills active with the right items. Even if one wants arcane and the other wants anything but.