OK, so if you run 'ps -aef|egrep dataserver' out in the OS you should see 2x 'dataserver' processes, 1x for each 'number of engines at startup'.
If you run a ASE command (dbcc checkdb) that requires just a single spid, then said command will run on a single dataserver engine (aka OS process) at a time. In process mode (only option available with ASE 12.x) the OS process will run on a single cpu, so you'll see one cpu worth of activity when running your ASE command.