Not being rude but i'm sure that a company as large has FedEx has done it's homework
One, they've probably found it isn't illegal, that isn't the same as being legal.
Two, laws can and do change.
If enough countries care, one line will suffice: No airline registered outside the EU shall be permitted to operate scheduled flights wholly within the EU.
Add some legalese to define terms such as "scheduled flights" and "wholly within" and FedEx can go home or sub-contract the intra-EU flying.
they're not the first international carrier to put a crew base in a country other than their own??
They're not but, discounting FedEx's HKG base for a moment, I am not aware of another carrier setting up a foreign base for 7th/8th freedom flying (except technically for QF's LON base - I understand they fly LHR-SIN/HKG/BKK and back - but at least the aircraft continues on to Australia)