It's pretty common in healthcare data, or at least the kind that deals with breadth of patient data. When trying to build knowledge about a disease by looking at a lot of patients, it's rare to get much useful info from a single source. Re-associating that multi-source data lends itself to a graph. If the company has been around for a little while, even if the customer-facing products don't use a graph database, at some point somebody has certainly tried it. (And once somebody has tried it, it lives forever in some part of the organization.)