I have been in many foreign jumpseats (all before 911) but have always needed a ticket. I’ve been on Sabena, British, SAS, Braeten Safe, Virgin, Mexicana, Olympic, Gulf air, Cathay, and just about every, national or larger, american carrier. I've seen all types of professionalism but the only crew to ever really concern me was a Southwest crew flying in to RNO. Still, you can't argue with SW's great safety record. They have some good sticks flying there. Maybe it's because they fly soooo many legs.
I tried to jumpseat on the Concorde one time. I walked up in my puddle jumper uniform and asked to jumpseat to London. I was told in a very polite, thick English accent, "Sorry sir, there is NO non-revenue on the Concorde." I didn't really expect to get on but you never know.
But back to the topic....I don’t know if it is allowed today but my experience is you need a tix to even get near the airplane. In London you won’t even know which gate to go to let alone be able to get to the gate unless you have a tix. Just another example, the glory days are over.