A dumb question from first time user:
From the specification of SCC-SG01, the voltage input range is -100mV
to 100mV. But if no signal/sensor is connected to SCC-SG01, is that
equivelent to RG = infinite so that voltage input becomes 2.5V/2 =
1.25V which exceeds the limit?
You are correct. The signal would be floating at 1.25 Volts, which would cause your measurement to rail at 100 mV. The SCC-SG01 has over voltage protection up to 28 V, so 1.25 V will not damage the module.