You can keep any armor you so desire. The reason the dismantling is recommended for Eververse items is because Eververse armor currently dismantles into Bright Dust. After the Eververse update happens that changes that system, Eververse items will dismantle into shards and glimmer. As Bright Dust is one of the rarer in-game currencies, it's recommended to get rid of any Eververse items that you don't wish to specifically keep. The armor, specifically, will be usable as ornaments to change the look of armor, so as such, isn't required to be kept if you just want their looks. Dismantling non-Eververse armor gains no benefits or penalties and has no changes with the system as it's always dismantled for shards and components.