I want to display a name on top of the hotbar in a specific empty slot, is this possible with commands?
In order to answer the question according to Nythcom's findings, you cannot manually put text where the names of items go when you select the item in your hotbar without a mod. Instead, use the title command to put text in the actionbar, which is above the space where item names go. This is the same place the texts "Now playing..." from jukeboxes and "You cannot sleep now" go, so be sparing with it if you want to constantly put a message there.
/title <player> actionbar <raw json title>
The title command uses json format to determine what text you want to put there. A useful json text creator can be found here.