Yep, that is the gist of it!
In Harris software, you have Conventional Sets and Group Sets for conventional frequencies and trunked groups respectively. Each one is tied to its own System in the radio. A system is just a set of parameters that define either the conventional set or the trunking system.
Conventional sets (in the Unity) can be any frequency the radio supports in any order. So you can have what your list shows plus some 7/800Mhz too if you want.
Group sets only contain GIDs for the trunked system defined by the system. It can't have any conventional sets in it.
Zones are unique in that they allow you to pull conventional sets and groups sets together to make a Zone list. So you would define all your conventional and group sets, then pluck from those lists to make a Zone. The Zone list is what the knob on the top of the radio actually scrolls thru, so because of that, you can have a P25 group right next to a conventional channel and another group from a different system next to that. How well does it scan like that? I have no idea, but I can't imagine it would work all the well considering the time it takes to scan the conventional channel, find and lock onto the P25 control channel, listen for a bit and then move on to another conv channel. But your mileage may vary, depends on how you set it up!
Hope that is a more thorough explanation.