From a Transaction is there a way in which to limit a users ability to create only "Inventory Items"? Currently on the pop up it allows for Assembly, Discount, Inventory, Markup, Non-Inventory, Other, Payment etc... etc....

Nope, not natively. I recently asked this same question to NS support and they said no. It may be possible with scripts/suitelets, but that is beyond my power to confirm.

Lame, you should in theory be able to restrict by role which types of item a user can create