Is the key group function the same as or a development on from the feature in the Drake system where a panel can place a key onto another users panel?

The simple answer is yes but the Key group function is a little more powerful, in that the Drake system you can only change one key at a time on one panel . The key group function allows you to change a number of keys on a group of panels in one step 
The Drake 4000 had a function called Rkey (remote key) which allowed either - special panel called a Router panel to assign labels to any panel that had an RKey on it . this was a key by key and panel by panel operation - Use ADM (or modern equivalent  is PM PRO) to assign labels to any panel that had an RKey on it, again you could only change one key at a time on one panel at a time - So if you had to change a RKey on 3 panels to be the same label : then you would need to select pane l1 and its RKey and change it , then go to panel 2 + Rkey and change and so on- you can have many Rkeys on single panel 

With Eclipse / Eclipse HX you have these options - From the standard user panel with the system config menu access enabled , .. you can assign keys on to another panel - From a Supervisor panel you can take control of a panel and do a local key assignment on its behalf - From PM PRO you can assign key groups: You assign a key group to a number of different panels then then you assign a label to that key group . All the panels in that key group will have their key changed in one step