While it is technically possible to add your Egnyte Archive Domain as a standard Content Source in the Secure & Govern application, some ramifications should be considered before doing so.
The Secure & Govern system downloads all of the files in a content source to classify them and search for sensitive content. Even though this download is within the same organization, it will still count against the egress limits set for archive domains, which could lead to additional charges for exceeding the egress limits.
When archiving files and folders, the system moves files from one location to another, essentially pulling them out of their original source. With this being the case, any file movement out of an archive domain (initiated via Content Lifecycle policy or on-demand actions) would count against egress limits set for the archive domain. Depending on the size of the archive job, this could lead to additional charges for exceeding the egress limits.
For additional specifications regarding archive domains, please see this article - Archive Domain Overview and Specifications.
For additional information regarding content sources, please see these articles - Content Sources.