I was able to duplicate this issue, and it looks like a couple minor issues worked together to cause it.
When you assign a server to a server group with the cPanel module, you need to assign it from right to left. If you don't assign a server, the server group uses none, and would be unusable with packages. However, when you create a package, the "Server Group" field is initally "Any", which loads your cPanel server, and sets a valid value for the "cPanel Package" field. When you change to a specific "Server Group", the module options should reload using a server from that specific server group. But due to #1, if you do not have a server assigned to the group, a separate error occurs, preventing the AJAX request from completing. This, then, does not update the module option fields as it should, and so you are allowed to save your package with a "cPanel Package" unavailable to the server group. Because no module is actually being used (none are assigned to the group), you get a "No host defined" error when trying to create a service.
This is now fixed in CORE-789 for v3.0.8.