I guess it depends on what you mean by “sensible”, or, how you would be trying to interpret such a comparison.
The ESS/time quantity is made up of 2 components (ESS and time). The ESS calculation will give you information about the amount of information you are getting for each parameter (e.g., the chain can very effectively explore different values of one parameter while being relatively “stuck” trying to find new values for another parameter). So the ESS of two parameter could be compared (again, depending on what you make of the comparison). However, the overall speed will be very dependent on the entire model (and your data). So differences between the ESS/time of a parameter in one model and the ESS/time of a parameter in another model may reflect differences in overall sampling speed (e.g., samples per second). So if one entire model + data reflects a more difficult geometry to sample from, overall sampling will be slowed and it will be difficult to compare the ESS/time of any parameter in that model to a similar parameter in a different, more easily sampled model.