I'll certainly defer to DCD and our more knowledgeable members, but I also have zoysia and have looked into dethatching. From what I've read, zoysia generally shouldn't need dethatching unless you're waiting too long between mowings (longer clippings don't break down quickly). Aerating every few years in the spring should take care of any thatch in addition to its other benefits. We just bought last October, so I'll be renting an aerator this coming March/April.
I'm also hoping the aerating will help the zoysia fill in a few thinner spots. My neighbor's clover yard (seriously, it's 100% clover) spread into mine and I have huge clover patches. I've read that zoysia will crowd it out when properly maintained. I know two applications of Scott's Weed & Feed hasn't done a thing.