I think the main thing would to make sure the folder structure is the same, e.g. for 10.2.x (and I think 10.3 is similar)
\arcgisserver\directories\arcgiscache\<servicename>\Layers\_alllayers\L00 (thru L12)
And that the conf.cdi and conf.xml files are set up correctly. Another thing to consider, especially if using the bundlex (compact version) is that they are compatible with the version of ArcGIS Server you are running. hey are different between 10.2.x and 10.3 in Server.
I would think those would be the only requirements, since in reality, the mxd for a Map Service with a cache can be basically empty. Unless you are need to identify or do other attribute/query type operations, the cache itself doesn even have to match the mxd (and is a trick on speeding up cached service for basemaps, etc).
I'm pretty interested in seeing if this works since I may try to take advantage of it too!