Yes it is possible

I have read in a couple of places that the 'Saxon Shore' ie the east coast was named as such because of the populations that had migrated there. These germanic peoples could well have peacfully living there for some time. The Raiders that arrived 4th Centuary came as small independant groups to loot rather than settle but from the same areas/tribes, in fact news of the opportunities for land, loot and glory may have filtered back to the homelands via traders on the east coast.

I still have a problem with such a small number of invaders completley replacing the indigenous culture so quickly. Even a fragmented Britania would have eastern Kingdoms (probably the most Wealthy) that had the resources to repel such small raiding groups before the became well established. Hence the theory that the peoples of the eastern kingdoms were in fact looking on the new arrivals as something other than invaders.