Both systems must have the 3rd party plugin installed. It’s no different to how fonts work. It’s a separate piece of software and it is required during previews and rendering.
As for 3D Premieire stuff, buyers know they need to have 3rd party plugins installed. This has always been the case with templates for as long as they have been around. Quite often, the template producer will provide pre-rendered layer/footage for the buyer to use. This is possible only if the 3rd party plugin plays a sort of a back ground role within the scheme of the template design. IOW, the 3rd party plugin is of course required but no further adjustments are required. It should be noted that if the buyer does have the 3rd party plugin then it is much better as he/she will be able to make adjustments, if they wanted to.
TypeGEMs – the Definitive Type Gizmo for AE
https://broadcastgems.com/typegems/
Intensive mocha & AE Training in Singapore and Other Dangerous Locations
Adobe After Effects CC ACE/ACI
Imagineer Systems (mocha) Certified Instructor
https://www.broadcastgems.com/mographintensity_shapestext/