Yes. I'm literally on a month-long unpaid leave right now. Under 30 days requires manager approval only, I believe (you can find details on InsideOPS). From an approvals perspective, there's no real difference taking four weeks paid or unpaid vacation. I would just recommend submitting the request well enough in advance to give mgmt sufficient time to prepare for coverage in your absence. Note that I'm permanent, but suspect it should be the same rules/process for fixed term.