Technically, you can both have a GCKey but from what I was told by the CIC, you cannot link the application to the Sponsors GCKey just the PA's. For the record, mostly everything will be on the PA side, except Sponsor approval. After Sponsor approval all updates are on the PA side of things.
Most stick to ECAS for updates and if you gave them an email in your application, the PA should get all updates and correspondence through that email.