You can cure 2 different kinds of weed in the same jar, but they will take on each other's tastes. That's not necessarily a bad thing, though, unless you are trying to preserve a particular strain's flavor.
I do it on purpose sometimes. I love when i have 2 different kinds that i think would mesh well, taste wise. Like a fruity weed and a piney weed. Or a fruity and a hashy. Or a skunky and another skunky. Or a strong flavored weed with a neutral one. I mix jars up and cure for weeks, or even months. Not with the main stash, but its fun to do with smaller jars, and get new, ridiculously awesome tastes.
One thing to consider, in my experience, is if you are mixing 2 weeds with different moisture content, the one with more moisture will bleed it's smell onto the one with less moisture. So it's good to make the heavier moisture one, the better tasting one.