You can go into Farm Site and use the Export option to export any layer using the "Export Layer" Export Type. Then in the Mobile program you can go to the File Menu and choose "Load Import Layer" and select the layer that you exported from Farm Site. This will allow you to use your Soil Type layer as a backdrop with the Farm Site Mobile program.
With regards to showing the acreage of soil types, if you go to the Layer Management box and choose your soil type layer in the Available Layers area and click on the Edit button. You can then add a new data field to be kept on the layer for the size of each area (be sure to use "Size" for the type). Then when you right-click on each area and choose properties or click on an area with the Define Area tool you can get the size of each area. At this point you can't get the size of all areas with a particular soil type, however this should be added in this fall's update.