No, that won't be sufficient, I'm afraid.
It must include ALL of the following details:
i) job title and current salary (or hourly rate and weekly hours worked if non-salaried)
ii) length of employment at the company
iii) length of time earning current salary
iv) type of employment (permanent, temporary, full-time, part-time etc.)
They will need to check the salary listed on the letter against his payslips to confirm that the amounts match. And whether he is salaried or non-salaried will affect how they calculate his income.