Not necessarily. When ECS only operation is granted, there can be requirements for removal of step boards and the like, which would prevent "in service" operation. That may or may not be applicable here. Likewise, no platforms need to have been checked for the Platform Train Interface for ECS only operation, other than making sure the train fits.
I don't know (well, can't remember!) - an earlier post said that they went via the Old Road, not Sheffield. That would make sense given the traffic levels on the two lines.
The Old Road is not cleared for 180's in either the Sectional Appendix or the undated "Open" NRSC (Network Rail Summary of Compatibility) documentation. However, if Hull Trains went that way previously, they would have been granted a temporary "Dated" NRSC, which would have detailed any prohibitions and restrictions - and is likely to have expired by now.