The Game Creators Store is being revamped with more support for Reloaded and new content being added- so you should perhaps wait till then. I believe we will be trying to get all old models from x9 to work with Reloaded.
I wouldn't buy the x9 packs expecting them to work in Reloaded. As we are doing a major script shift from FPI to LUA. Meaning your zombies just won't work the way they should once brought into Reloaded since they arnt using LUA.