The Newer Versa Note Hatchbacks ( maybe 2014 to present) have an underbody spare ( compact spare) which is actually under the car suspended on a rack. Inquired and several people told me it's OK to just put the spare tire ( steel rim ) in the rear trunk area inside the car and behind the 2nd seat.

It would be raised a bit as the area there is hollowed out a bit but not shallow enough to fit the compact -spare tire .

Thinking it over, wondered if this would present a safety hazard as the tire would be unsecured ???

mac, the safety hazard part ABSOLUTELY correct , mostly because it will ALWAYS BE THERE & LOOSE - unlike the occasional bags of groceries and such. Now the sheet metal in the rear "Deck" may be very suitable to route heavy rope/jack-chain from cutouts in heavier gauge sheetmetal in back and ran through centerhole of spare and mitigating ,well, the fear and hazard of "missile" inside your car during a 70+ mph accident ?

From the Owners Manual page 6-5 for the Nissan versa Note 2016, the procedure to use the underbody spare is extensive and detailed.
Must have tool and strength to turn bolt.
How to lower the rack, remove it from hook, clean wheel and hub and be sure to repeat procedure and return rack to position after use.

Is this not a bit much to expect from a stranger or others who might offer to help ?

Even the ASA road service gent will be annoyed.

mac, yes , know what you mean , and I stow the spare & little scissors jack (sometimes I bring my "superlight" aluminum Hydr. one) , loose but tied to pass. side sheetmetal like above ,in trunk. I have been able to get it started - under the car in like 3 short minutes , as long as a LOT of stuff not on top of it !

Unless you're going offroad I don't see how significant the hazard of an approx 30 pound disc floating and coming right at your noggin is. There are enough obstacles to keep it secluded in the trunk area, and it should be heavy enough to stay down unless you go over serious bumps and potholes at speed.
At worst, you might be more annoyed by the sound it makes if it were to bounce around.The only thing I ever hear is my lug wrench if I hit one of those bumps... if at all. It is more likely to slide around in silence.

Although I have not had to use a spare donut in an emergency since 2009 or so, I still check the air pressure and like to keep the trunk clear enough so everything is accessible.
Nissan probably cared more for the usable storage to be claimed in the magazines. You have your priorities, I'd say go for it.

Btw, it's pretty nice that they still offer some kind of a limp-home wheel rather than fix-a-flat and a pat on the butt.

If you rearend someone you mat get a whopping lesson in how much inertia a spare has. I've seen one tear through a back seat upper before. It DID get trapped by seat spring wire but almost got 100% free. People have been killed by them before. It depends on the sheetmetal strut configuration that goes over the big slotted hole there, some cars have nothing there and the tire goes right through, some have a middle divider and much harder to then.