Has anyone managed to integrate Sage Evolution into Purecloud Engage in order to screen pop the agent desktop?

Andy,

You might want to consider PureCloud for Chrome.  It's not a direct answer to your question, but it's a client integration product that we intend to be broadly applicable to web-based systems that agents are using.  More information on PureCloud for Chrome, including information on screen pops, is here:

http://blog.inin.com/keep-customers-in-full-view-with-purecloud-for-chrome/#sthash.c21QIK3Y.dpbs

Thanks!

Additionally, there are integration opportunities for data actions leveraging the web service data dip connector: https://help.mypurecloud.com/articles/about-web-services-data-dip-connector/

While not a direct integration to Sage, this connector allows for a great deal of flexibility to access data from arbitrary stores as part of your IVR call flows and agent scripts.