WGS_1984 or state plane projection , both works.
How to publish map service as WGS_1984( 3857 ) on arcgis server?
Simply check the tiledMap check box, when you publish map service.
If you do not check tileMap check box, by default, it is unchecked. You will get a state plan projection for your map service on arcgis server.
That is the way how ESRI set it up.
If you check tiledMap check box, because the tiledmap will work with google maps, bing maps, apple maps, openlayers,
All those web map use same projection wgs_1984 ( 3857). So arcgis server will automatically re-project from state plane to 3857.
For example, all my layers in ArcMap use projection : state plane california zone 6 (2230)
If I did not check tiledMap checkbox, after I publish all layers to arcgis server, you will find all layers still use original projection 2230.
If you did check tileMap checkbox, after you publish, you will find all layers now use 3857.
Some city's map service use 3857, some city's map service use their original state plane zone xxx. Both works on this website.
Because I setup automatically convert between 3857 and state plane projection. If your map server is 3857, I do not need convert. If your map server use state plane, I must convert all the coordinate from your state plane projection to 3857 before I can show it on google maps. Remember that all the web map are tile based, use the same wgs_1984 ( 3857) projection.
Geocoding Server is different story.
If my reference Roads layer is 2230, I create a address locator, then I publish it as geocoding service, I always get a 2230 on geocoding service.
If I want a 3857(wgs_1984) geocoding service, what I do?
Easy, first you should re-project your reference Roads layer from 2230 to 3857 use arcTool box, data management tool, project.
Then you create a address locator, then publish it, you will get a 3857 geocoding service.