I don’t think this is a validation, but a simple link back to the Google Scholar entry (usually with an identifier such as PMID or DOI). There is however no guarantee that the entry exists.
We do the same within our publication repository, see e.g. Rosuvastatin and cardiovascular events in patients undergoing hemodialysis - Zurich Open Repository and Archive (Google Scholar link in section “Citations”).
Also, there are other commercial (Scopus, Clarivate Web of Knowledge), semi-commercial (Dimensions) or non-commercial (Microsoft Academic) databases that provide well-documented and extensive APIs to get citation counts and other metadata. The problem with the commercial citation databases is, that every publisher needs to have a license to get access and an API key - for many publishers, this will not be affordable.
The easiest thing would be to implement the Dimensions citation batch into OJS by way of plugin or template that reads the DOI. MA would need more work, for Scopus and WoS I think it is not worth to start development.