Can I let someone upload photos but not delete anything?

Yes, you can do it by inviting them as an Editor and switching off deleting for Editors. Invite them to the tour as an Editor, then in My Account open Client Workspaces and, under Action Permissions in the Editor column, untick Enable deleting panoramas. It applies to the Editors of all your tours. An Editor can still change panoramas, floor plans and hotspots. Choose what Viewers, Editors and Admins can open has every box.