Dave; The earlier Insteon SwitchLinc Dimmers did send a %dim.
An older 2486D KeypadLinc Dimmer and a brand new I2CS 2477D Dual Band SwitchLinc Dimmer both seem to send Bright and Dim commands.
I forgot to log the new 2477D
Older Hardware Revision 1.1 2876DB Icon Dimmer Switch
R: B1 - 3:13:20 PM 7/28/2012
R: BOn - 3:13:21 PM 7/28/2012
R: B1 - 3:13:22 PM 7/28/2012
R: BOff - 3:13:23 PM 7/28/2012
R: B1 - 3:13:26 PM 7/28/2012
R: 29% Preset Dim 3:13:26 PM 7/28/2012
R: B1 - 3:13:42 PM 7/28/2012
R: 45% Preset Dim 3:13:42 PM 7/28/2012
R: B1 - 3:13:58 PM 7/28/2012
R: 6% Preset Dim 3:13:59 PM 7/28/2012
Older Hardware Revision 1.4 2486D KeypadLinc Dimmer Switch
R: B1 - 3:21:00 PM 7/28/2012
R: BOn - 3:21:00 PM 7/28/2012
R: B1 - 3:21:02 PM 7/28/2012
R: BOff - 3:21:02 PM 7/28/2012
R: B1 - 3:21:04 PM 7/28/2012
R: BBright - 3:21:04 PM 7/28/2012
R: BBright - 3:21:04 PM 7/28/2012
R: BBright - 3:21:05 PM 7/28/2012
R: B1 - 3:21:27 PM 7/28/2012
R: BDim - 3:21:27 PM 7/28/2012
R: BDim - 3:21:28 PM 7/28/2012
R: BDim - 3:21:28 PM 7/28/2012