The correct answer for sure is "it depends on the exact model" but that is quite useless ;)
As far as I can see all the airbag vests deploy over your whole shoulder area. This is definitely not suited for backpacks.
For some avalanche backpacks it is possible to have one airbag unit and multiple matching packs, e.g. Ortovox. I have not done this myself as I do own any airbag system but that is at least what they claim. This would still be a vendor lock-in but at least the backpacks without the airbag unit are quite cheaper.
A note of caution on using a vest instead of a backpack. An airbag is considered just the last line of defense. It does not guarantee that one stays on top and you should never go into avalanche terrain without the standard avalanche set of beacon, probe and shovel. The vests do not really look like they are suited to carry a probe and shovel. Therefore I would discard them for the idea of "just skiing". They might be OK if you have a snowmobile with saddle-bags however.