Is it possible to delete feature/raster data after the cache is built?
The idea is to built cached orthophoto service from raster catalog and then erase the catalog to save space.
If you are asking if you have a raster catalog that you want to build a cached map service from and then delete the raster catalog to save space then the answer is yes. As a cached map service does not require access to data after the tiles have been generated. But I hope you plan to maintain a copy of the data say on an external HD or something in case something goes wrong with the map service latter or you need to access a particular image at a later point.
I agree with Robert, the data isn't needed once the cache is created (assuming you don't plan to update often)....but keep a backup of the data if you can.
Other suggestions. Make a backup copy of the .mxd for the service (just in case. Then edit the original (i.e. the one the service points to) and remove all the data pointing to the "deleted" raster catalog (data) and replace it with a simple layer that is the same extent (even if just a extent box). This may help in the long run if zooming to extent is a factor, and removing all the broken links may speed up the use of the service.
Another nice trick, since about v 10.1 or 10.2 (I think), is you can copy the entire cache folder to another location and users of ArcGIS (the same version or higher) can use the cache directly, without going thru the service. This is a nice option for remote locations that may not have reliable internet.