Try to use this (run from the terminal and implement in nagios if you like it):
./check_procs -a backup -c 0:0
(of course you have to be in a directory containing check_procs executable)
0:0 critical threshold will issue critical alert only if output is out of specified range, and since we've set this range from 0 to 0, if no process is running it will return an OK state. If there is 1 or more processes running, it will issue critical state.
-a switch defines the strinh which to serach within processes.
you could also run:
to see all available options of a plugin