So others can know, I just spoke with ETC Technical Services regarding this. I was told that the ThruPower module can be configured via the Concert software to be in Switched mode to use its relay function. It appears that the option to be in Swiched mode for the ThruPower module is not the same as being in Switched mode on a D20 dimmer module. Switched mode with the ThruPower module activates the relay as opposed to the D20 in switched mode which still delivers power thru the SCR. A couple of documents I read online said, regarding the D20, “It is important to remember that even in Switched or Non-Dim modes, when using a Phase Controlled Dimmer, the sine wave is not a pure sine wave” and “there will always be a modification to the voltage waveform as the dimmer turns on even if it is attempting to fire at full.” I also read that “Instead of designing their fixtures to operate on dimmers that are set to full on, they (other manufacturers) void warranty if the fixture is powered by a dimmer set in switched mode. In contrast, ETC's Selador series LED fixtures are designed to be capable of running on a dimmer in switched mode so, within the ETC family of LED products, no damage will be caused as long as the fixture is not powered at a dimmed state.” I read further that “ETC recommends that loads such as LEDs, Moving Lights, and Motors be powered via a non-dimmable source such as a Relay or Constant Current Module, or a ThruPower Module set to Relay mode.” As you can tell I was concerned that I would damage my non-ETC equipment if I ran the ThruPower in Switched mode. Apparently this is not a problem since the power is delivered through the relay in Switched mode, not the SCR.
Also I should mention that the model number I mentioned in my original post is incorrect. The correct model number is TR20SAF.