You are confused. No one is allowed into the country for "10 years". The maximum is 6 months. The 10 year visa simply means one has the permission to fly to the US at anytime during a 10 year period. Once in the US if such person can convince Immigration of only coming for a temporary visit at the end of which he'll leave, will be given leave to meter for 6 months. Cannot work. Doing so is a violation of his status and exposes him to being placed in removal proceedings in immigration court if caught.
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Why are you interested in these questions? If you are providing him with employment, you have set you up for a lot of trouble.
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The visa is valid for ten years but the visit is not. The ten year visa is good for multiple entries. However, the law permits a visitor to enter the US for only a period of 6 months. That period can be extended typically for 6 months. A visitor is not allowed to work in the US without work authorization. He probably does not have it.
The answer provided here is general in nature and does not take into account other factors that may need to be reviewed for a more precise answer. You should consult with an immigration attorney before taking any action. The answer here is not intended to create an attorney-client relationship.