Most systems I have seen use multiple probes with an averaging function.
I believe on some Pratt Canada engines, the ITT is "synthesized" (sp?) in as much as temperatures are taken at two discreet engine stations and an analog computation infers the temperature you are interested in. The engine I work with at the moment has three or five T5 probes (dependant on version) with an averaged readout to the flight deck. Should a probe go bad, your average becomes a little less accurate but is useable (in fact as an operator you wouldnt necessarily know a probe had gone down).
Also it is not used as part of the engine control loop until you introduce the pilot into the mix - Mark 1 eyeball and control of the N1 lever!!