Can I use pickled kimchi instead?

Kimchi is by definition a sort of pickled product, fermented with salt instead of vinegar. Your jarred version would be perfectly acceptable, so long as you like the way it tastes- that's all that will count. Just scoop it from the jar and drain it in a sieve, then squeeze it as dry as you can and proceed with the recipe. Kimchi is more of a class of preserved veggies for Koreans, and it's made with lots of different veggies besides the usual napa cabbage. Kind of like the term "salad" in English, we don't mean only things made with iceburg lettuce. If you like to eat it, then use it.