your right, however, it'd add a very very small amount of distortion - in the same way an LA2A or 1176 does.
In fact, all the classic compressors monitor the output in the same way.
You could put an active buffer accross the output (secondary of the transformer) however, you do potentially spoil your galvanic isolation.
Regarding the digital relay switches, the controller can be used for anything. It essentially debounces the switches, and outputs 3v3 levels to drive the LED and another target (such as a relay card). You can use the controller to drive either the differential signal relay card, or the single ended relay card. (http://www.expataudio.com/expatshop/index.php?act=viewProd&productId=10)
You can also very easily create your own relay circuits - the circuitry to drive 3V3 to a 12V or 24V relay is very simple.
/Rochey