It’s in the general terms by Google: https://policies.google.com/terms under which also Google Scholar falls as service (see their list of services). Google content is copyrighted - you can use it, but I’m pretty sure that this means personal use (as covered by the copyright law).
This is why we don’t include citation counts in our repository (just a link to Google Scholar).
You can include e.g. Scopus or Web of Science citation counts in the case your library has a license with Elsevier or Clarivate, which allows to access their APIs.