You just don't get it, do you?
The whole reason EMT are having to hire in is because their HST fleet is committed to additional trains that day, associated with the southern West Coast engineering works. They do not have the resources to run extra services for the benefit of Class 66 scratchers, which would be financially dubious to say the least.
Err no. I get it perfectly well thank you very much.
I am fully well aware of everything you've said, however the key issue you don't seem to get is that the resources to operate these trains are not EMTs (possibly with the exception of a couple of revenue staff). The locomotives, the coaching stock, the driver(s), and the guard(s) will not be EMT.
Therefore unless there is an operator with all these resources
in Derby then they will have to have an ECS run from somewhere. The best way EMT could avoid the service train being full of enthusiasts is to give them another opportunity. Run one or both these legs as a service train/mini tour, and I would suggest 80% of those enthusiasts who would otherwise be filling up the Skegness service would switch to these, therefore allowing the hire in to deliver it's intended benefit.
Now tell me what EMT resources would be required?
Financially the moves would have to happen anyway to get the stock into position. The crew would have to be present. The only cost is the marginal cost in track access charges of a class 1/2 over a 3/5, if enough tickets could not be sold to cover that I would be astounded, and anyway even in the highly unlikely situation it doesn't then you are still benefiting from reducing the demand for your specially laid on Skegness services.