aysewnur Yes, anything you own in Epic should work with the EA App. When the tie-in was first available, players reported that they had to launch Sims 4 through Epic one time to get the EA App to recognize whatever they owned in Epic, but after that, they could install and play the content through the EA App without needing to involve Epic at all.
I will say though that EA also offers expansion packs for 50% off quite frequently. So unless the regional pricing is better through Epic, you could also just wait for the next EA sale, which will probably start Black Friday week or a bit before that.