Ability Hotkeys

Is it possible to hide the icon of a unit ability, while still making the ability accessible via its hotkey?

If so, how would i do it?

No.

Kinda...you could make the icon have a black or transperant icon.

No, you cant, if the ability isent on the any of the ability slots the hotkey wont work.
If you make the icon transparent or black, it will still take up a slot and you can hover over it and it will show details about the ability still

While I worked on THief of Dalaran...I solved that problem by alpha-ing out the tooltip box and all the words associated with it but im guessing in your case, you cannot do that. oh well...lol

Just disable the GUI entirely, then no tooltips show up ever. The problem of course is if you want only one ability to be hidden. I have made a full command card appear to have no abilities before easily.

Once you do that, doesn't it disable selection too? I don't know for sure but...

No, you diable selection with 2 other triggers.