I wouldn't rule out a native, undersea ETI civilization
Volcanic vents provide smelting opportunities. If the ETI is octopus-like, then it can manipulate tools. If not, there's possibly some octopus-like animal that the ETI could train to manipulate tools. If something absolutely needs to be done in the air, it could be done on rafts of vegetation or on ice caps, both of which provide a way to get out of the water on an all-ocean world.
And they'll have tens of millions of years of continued natural selection to get smarter than we are now. Who knows what they could come up with.