Your Keyshot for Alibre Design is activated from your Alibre Design activation - there is no Keyshot serial code. The information from Keyshot applies to separate newly purchased Keyshot 8 licences, not bundled products, nor pre-existing licences.
Based on previous experience, it seems likely that in due course Keyshot for Alibre Design for those with current maintenance of Alibre Expert at the time, will be updated. I would expect that to be some time after the official launch of Keyshot 9 (date not yet known) and may coincide with an Alibre product release.