This is a tuff question, in my opinion. For a thermocouple or RTD that is used in connection with a Meter, Instrument, or Relay, then 501.105 should come in to consideration for its impact on the suitability of the equipment as a whole for CID2 locations. But after reading 501.105, I am still not sure that you will find justification there to use the RTD or T/C in a CID2 area.
The obvious argument for me is tha the use of the T/C or RTD does not affect the suitability of the equipment as a whole to be identified for a CID2 area. The burden of proof would be on the manufacturer of the equipment to prove to the AHJ that equipment as a whole is suitable per 500.8(A)(3), which states that the manufacturers self evaluation is adequate to determine suitability of identified equipment.
In summary, you will probably not find explicit approval in the NEC to use T/C's or RTD's. So at that point, since it is not explicitly prohibited either, then you have to provide evidence to the AHJ that it does not make the equipment as a whole hazardous for CID2.
T/C's and RTD's are probably hard to find listed for CID2, so these would probably not be hard to justify to an AHJ. Whereas most other electronics do come listed for CID2, so it is best to use them and not have to explain to the AHJ why you can use them.
