This looks like the interop libraries auto generated off the Office OLE Automation interfaces. SafeArrays should have existed back then. I imagine this was used instead for perceived developer friendliness vs forcing developers to box up and create a Safe Array to marshall in (more boilerplate).
Don't think it works in this case. In general why there are so many overloads in C# with parameters like arg0, arg1, arg2 and so on is because of the poor performance of the params solution for value types.