Well, how sure are we that Loki's using Observation Haki, in the first place?
There is another power that could explain how Loki can see with bandaged eyes, and that's the Voice of All Things. And actually, that might fit his character better, given his friendship with the Elbaph animals. And as far as we know, I don't think VOAT is affected by Seastone.
I don't know. It could be a little bit of both, at least.