Higgins' dogs Zeus and Apollo are guard dogs for the estate, part of the estate's security. Magnum's job at the estate is as a security consultant. Both being security, the dogs should be working closely with Magnum regularly, as opposed to always treating him like an intruder.
Even though this show has only 5 seasons, it is listed as being available to WATCH NOW on PLUTO for seasons 1-8. That reference is for the original show not this one.