In order to take the deduction the vehicle has to be used at least 50% for business purposes. The vehicle also has to be acquired for business use.
The business that buys the vehicle would be the one to get the deduction. If you end up sharing the vehicle, that would limit the business use percentage for each of you.
So let's say your husband's business buys the vehicle in its name. He uses it for business 80% of the time and you use it for business 20% of the time. (Assume you have separate personal vehicles and do not use the van personally). Your husband could take the Section 179 deduction x 80%. Your husband could also deduct 80% of his actual expenses (he wouldn't get the standard mileage deduction because by virtue of taking 179 you are choosing to deduct actual expenses). The time you are using the van is a non-business use of your husband's business. You would not get any of the 179 deduction because your business did not acquire the van (and you are using it less than 50% of the time), but you can deduct mileage or actual expenses for your 20% of the use that you have accounted for.
If you are both going to use the van, it makes sense for the person who will use the van the most to make the purchase through their business. Your net incomes will be combined for income tax purposes (but not SE tax purposes), but the business/personal break down will effect the total deduction.
Keep good (and separate) records!