Visa on arrival to Vietnam 6 month

I will be visiting Vietnam for business reason. I'm South African residing and with employment in Australia holding South African passport. My Australia company has a joint venture company in Ho Chi Minh City and I'm required to be in Vietnam for 6 months to stand in for an employee who will be on extended leave (6 months). For the 6 months duration, I will be returning back to Australia at least twice for around 4 days each. In my situation where I will be in Vietnam for a total duration of 6 months and for at least 60 days at any one time in between travels, could I apply for 6 months multiple entry visa on arrival for business reason.