What is the role of a Japanese trainer and how should they be used in the corporate setting?
Japanese trainers should be used to teach TOEIC (excluding the speaking parts). Why? Because they know and understand the students' feelings and their weaknesses. They can also share strategies that the "average" Westerner doesn't have a clue about. Do not request a Westerner as your TOEIC trainer, unless they are specifically qualified, which 95% are not. You can use a DVD to listen in class if you want some listening practice, the same type of resource that you will have in the actual TOEIC test.
Japanese trainers can also be used to teach lower to mid levels conversation at the corporate level. However, ONLY ENGLISH can be used in the class room. Japanese trainers teaching Japanese students, English, using Japanese, defeats the purpose of learning a language. It's ridiculous! The student becomes lazy by not learning how to think and speak in English and will become dependent on Japanese as a crutch.
They will remain in the Japanese mindset of always translating before speaking, and while listening to the conversation. This will not work in the long run, so please avoid.
Students must be immersed in their target language in order to make REAL progress. When they're traveling overseas, no one will speak Japanese to them. Students' MUST learn to deal with unknown situations in English. Think in English and use English to solve problems.
Japanese trainers do have a place in the ESL and EFL class room, but it must be done optimally.