Recoverable probably yes.
Droppable not... the definition of "fixed" is "not droppable".
Anyway, I still don't get what you really want to achieve... do you just want e.g. that Heavy Plasma can be used only by Sectoids? If yes, that's quite silly, isn't it... what would the game do if you tried picking up Heavy Plasma into your hands? Just say "cannot pick up this item"?