A lot will depend on location, climate and local codes.
If those speakers are installed between a basement and main floor, or a main and upper floor, no harm will come likely, although you have sound bleeding through the space, which I would not favor. Speaker wires should always be in conduit in any event.
The trouble will come for top floor use, below the roof space in the colder climates. You will have a building code issue for sure.
My AV room is in the top floor below the roof, in Minnesota. I could not install those speakers in my room without an enormous expense and hassle.
It all has to do with improved insulation codes and preventing troublesome ice jams, which are a huge problem in the snowy colder northern states in winter.
The thinking on this and code changes have evolved for the better over the last half century.
Basically the current codes, which are correct, are to have a cold roof, and the colder the better. That means the insulation has to be right above the ceiling. Code here in the twin cities requires a minimum of 14" of blown insulation over the entire ceiling. Then there are eve ventilators, connected to "pop vents" which exit above the blown insulation. There is no insulation directly under the roof. The cold air is thrown up to the roof. Codes have also changed as regards roof pitches and steeper pitches are now required. This allows snow to fall off and water to drain quicker and not get dammed up and cause ice jams resulting in water leaks.
This problem requires careful design in the snow belt. Every winter ice jams are a headache. This results in people going up onto their roofs to shovel off the snow, slipping and falling to the ground. This results in death or severe disability as a rule, and there are some every winter.
In my time in the ICU in Grand Forks, we had some brain death declarations every winter from these events. A very nice guy who had an upscale B & B in Benedict MN where we had our former home, fell off his roof clearing snow, and now is paraplegic and wheelchair bound.
I had a huge problem with ice jams when I first bought our lake home. The pitch of the roof was typical of its early eighties construction. I had a huge ice dam problem, so I had the eve vents replaced and put in 4' pop vents and had 2' of blown insulation blown in all the attic spaces. That solved the problem.
My studio here, and the one in Benedict were below the roof, and so neither would have been suitable for any ceiling speakers not totally enclosed.
You can see two of the back boxes for two of the ceiling speakers. The conduit was run and the boxes placed before the ceiling sheetrock. Then the ceiling insulation was blown after the building passed its pressurised air leakage test.
So if you were to install ceiling speakers after the room was complete, you would have a huge headache and a lot of expense, which would make them even more outrageous as to cost.