That's not actually true at the domestic level. The KKK, the Kurdistan Workers Party and the PFLP never had material support from abroad. Neither did the Tamil Tigers, for that matter.
I wouldn't really call the KKK a terrorist movement.
I don't know anything about the funding of the KWP, I'll skip that one.
PFLP--all the terrorist movements over there had Islamist funding.
Tamil Tigers--originally from India, later from extorting Tamils that had moved elsewhere.
The only problem with this theory is violent fundamentalists don't actually disguise themselves as refugees for infiltration purposes; it would take them YEARS to establish themselves in their new community well enough to actually begin planning attacks like we saw in Paris.
Some of the Paris attackers came in pretending to be refugees.