Positive voltage with an inverting buck boost
Yes, if your load is isolated you could hook it "backwards" across the output of an inverting buck-boost.  

The reason you find non-inverting buck-boost converters is because often the load has to be referred to the same ground as other rails in the system, and you can't connect its ground to the negative rail and positive to the system ground.

For example, suppose you have a microprocessor that runs from a battery.  It also needs a 3.3V rail for some I/O.  You could use a buck-boost from the battery to generate the 3.3V, but it has to be referenced to the same ground as the battery and the uC.  Therefore you need a non-inverting buck-boost.

The non-inverting buck-boosts have the disadvantage of needing 4 switches, or in some topologies a capacitor that has to handle the full load current. (e.g. SEPIC)