According to Esri documentation, geodatbaase replication is RDBMS agnostic, meaning that theoretically there is nothing to prevent one from successfully implementing geodatabase replication between Oracle and SQL Server.
"Geodatabase replication is built on top of the versioning environment and supports the full geodatabase data model including topologies, networks, terrains, relationships, and so forth. In this asynchronous model, the replication is loosely coupled, meaning that each replicated geodatabase can work independently, and all changes can still be synchronized. Since it is implemented at the geodatabase level, the DBMSs involved can be different. For example, one replica geodatabase could be built on top of SQL Server, and the other can be built on top of Oracle."
Has anyone in the community successfully set this up? If so do you have any advice for someone how is considering going down this road?
No I haven't even tried setting this up yet because I wanted to get opinions from folks who have actually gone through it before. What is theoretically possible and what is advisable are often not the same. But in the end this discussion has been overtaken by events. I've just been informed that my organization is phasing out Oracle as its primary RDMS platform and moving towards SQL Server. So it looks like I'll be replicating SQL Server to SQL Server anyhow. Thanks for your reply.
I never personally setup one like the above mentioned scenario, but surely I have seen a few customers using this kind of setup while working in Tech Support. So yes, this is possible.