They support PGP keys, but I don't think anything in the keybase UI or proofs will reflect key certifications made in PGP's web of trust. You can "track" people, but that's not the same thing.

It should be possible to augment the existing proofs with the WoT relationships, which could be valuable in a small number of cases.

However, it wouldn't surprise me if more people started using Keybase because of this one blog post, than have ever used PGP's web of trust features.