I am sure it is, but the question is when the fix will be in place. TPE needs to get its units into service quickly to deal with overcrowding. If their Hitachis can run on diesel for now then that is a blessing, except for the emissions obviously but that at least will be temporary. It would also be an unplanned benefit of opting for bi-modes. They will have passed the resilience test from the off!
To my knowledge, no, diesel or electric power both have the same issue because the interference comes from the traction motors, which are in use whether or not the unit is on AC power. That's why the interference suppressors are going in every vehicle, not just the one with the transformer in it. On that basis, every unit will need to have been modified before it can enter service. Whether the modified units will be permitted into service before the trackside work has been completed I'm not sure yet, I imagine it depends how long the trackside work takes.
I'm pretty sure as far as 'signalling interference' goes, this is the biggest job yet in terms of how much needs to be done to put it right. It will not be a quick and easy fix as some have been before. Millions is being spent on this and the weight of each unit is going up by multiple tonnes to bring the interference into spec.