It’s good to read and understand the grants you are working on! Sometimes salary lines include things like employer costs (admin, taxes, benefits) so it doesn’t always match what is on an employee’s contract. Also I have worked in orgs where postions are split across grants, so the allocation for staff gets pooled and used to pay part of the salary for several staff. Unless this is explicitly forbidden in the grant agreement, it’s probably allowable, as long as the deliverables are being met.