No. AddOns are global.
Some provide functions that you don't have to use though (e.g. if it provides a macro called "penguin", you don't have to actually use that on a page in any space)
As an example, most of the theme addons require that you choose to use them on a space-by-space basis (or set them globally, but you can still turn them off by space). And some addons have functionality that limits their use to selected spaces in other ways.
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