It should be possible.
If you are writing C++ class, remove the U prefix for your UItem class (eg: USomeWeapon → SomeWeapon)
If you are writing a BP class, add _C postfix to the blueprint asset name (eg: BP_SomeWeapon → BP_SomeWeapon_C)
Note however that for blueprints it is not guaranteed to work as it will only find classes for assets that are already loaded in memory. If they are not, you’ll have to load then via a call to LoadObject or LoadClass (or the async load methods), and they require full asset path.