From a pure Insteon point of view, a Scene/Group initiated from a button or paddle press will be under control of a single command so you cannot DIM some devices in the Scene/Group and BRIGHTEN others in the same Scene/Group. You can set a low “Brightness” level in a particular device when you set up the Scene/Group link for the device. Then when you do a Scene/Group ON from the button/paddle controlling the Scene/Group, the device will go to that low brightness level, even from a full on. Has the appearance of a DIM but it is really an ON to the lower brightness level. I just tried that with a Lamplinc so I can confirm from actual experience that it works. One button on a Keypadlinc turned the lamp full ON, another button with the lower brightness level Scene/Group link turned the lamp ON to the lower level brightness from a full ON.
Perhaps a button/paddle press could run an EZServ macro which dims devices in a “Dim Device Scene/Group” and brightens devices in a “Brighten Device Scene/Group”. I’ve been using Insteon in the house for nearly two years but only just started using my EZServ so I’m reluctant to respond to questions from the EZServ view point. You should update your post with the level of the image running in your EZServ.