I've opened 2 salary account till date, Canara previously and Union most recently,
I both cases my employing organization told me go their branch with Joining letter and other docs,
For Canara they even called the branch manager to expect me and help me out
So i think Joining letter is required, salary Slips might work if have joined long back,
This ofcourse is for PSU banks
For private you can just open and open a salary without anything and as long as Salary gets credited every month you'll keep on enjoying benefits of that account type