The programmable Group Presence key can be used for ACD if you use "Hotdesk ACD". Just use the "agent skill group" number on the directory number field when you assign the key. Also make sure you set the correct group presence settings in the COS for that ACD user so the user can toggle it, since in a default COS setup you can't if I recall correctly.
You can not program it as a key on a ACD enabled device (read phone e.g. 5324 with ACD enabled) but you can use the feature access code for the logged in "agent ID".
Since that makes it a hassle for the user, I would prefer a "Hotdesk ACD" any day since at that moment it consumes maybe a license for the agent, but you can also use the extra functions like group presence as a programmed key. It also makes the system only consume as many ACD license, as there are concurrent agents logged in, which kinda complements the "IP device only".
Hope this helps.
Roel