How to link spatial and nonspatial data that is housed on two database servers?

I'm working on a proof of concept.

We are building a web map application where the data is split across two different database servers. The geometry is on ArcGIS server and the attributes or business data are on a remote SQL Server instance

Does anyone know to link query the data across two database servers?

One idea is to use REST webservices to communicate with the two separate datastores.