Mentioning a published paper from a current team member in a PhD letter application
I think the content of the publication is more important than the author of the publication.  I would mention the paper as well as other similar papers that you have read that are by other authors.  Most likely, your  person "A" will know of the other authors in your field so it is not necessary to soley focus on mentioning person "A."  I think it is more important to show your interest in the specific research area rather than knowing where person "A" worked.