I saw a house with an expansion valve rather than an expansion tank. Would the same rules apply to this valve’s drain pipe that apply to the TPR valve: No threaded end, 6" above the floor, etc.
The inference is ‘YES’ the same as a TPRV… https://youtu.be/bmmUGze-xPA
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There are many requirements for a TPRV and the rules do not apply to the thermal expansion control valve.
A safety relief valve is not the same as a thermal expansion valve! One has very hot water discharging from it and the other has a small quantity of cold water discharging from it.
Follow manufacturers installation instructions and note to the home owner pressures of 125psi may build before the valve opens.
Sorry no YouTube plumbers here 
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Since the expansion valve would only have “a small quantity of cold water discharging from it,” I wonder if it would be acceptable to run its discharge line to the water heater drain pan or T it into the drain pain discharge.
It needs to be ran independent of the relief valve discharge piping. Running it into the pan is fine with an air gap. You can’t tap it into the pan drain because now you’ve mixed a potable water connection with a sanitary drain connection.
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