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Yes he would need a work visa or a visa as an expert on temporary basis before entering the country (a visitor to Saudi Arabia cannot obtain visa upon arrival at the airport). But in both cases his passport would have to be physically stamped by a Saudi embassy based on a request from his employer or agent before traveling.
Regarding the last part of the question, yes a company can obtain a work visa for its employees if they are working temporarily in Saudi on visitor's visa.
Hope this answers your question.