You can get a decent score using simpler words / language, but probably not a 6. The TOEFL is designed for non-native speakers, but the GMAT is also taken by native speakers. The very top score (6) is reserved for essays that "have it all" - including pretty much perfect grammar and spelling using sophisticated language.
But a 4.5 or higher is considered good enough on the GMAT - as long as you score in that range, you're fine.
Please also see my response to your other post here:
please-point-out-flaws-in-my-issue-analysis-t11228.htmlAnd you may want to read this article:
http://www.beatthegmat.com/mba/2009/12/ ... -no-thanks