The Anon I replied to alleges that addons cover extensions (ABP, Betterprivacy, Ghostery, Skype, etc.) AND plugins (Flash, Shockwave, java - anything that uses the NPAPI).
So if my initial interpretation was correct (same as yours- this is for extensions not plugins), that won't be a problem; if his interpretation is correct (keeping in mind that he challenged mine - plugins/extensions are under the addons umbrella, both appear in the addon manager, etc.) it would be.
I guess the only way to find out will be to install a copy of the beta and then a plugin or two.