"check swap" should already be defined in your commands.cfg as:
# 'check_local_swap' command definition
command_line $USER1$/check_swap -w $ARG1$ -c $ARG2$
which means your service needs to be:
use local-service ; Name of service
template to use
service_description Swap Usage
notice thta you are calling check_swap instead of check_local_swap, and the different usage of the -w and -c parameter, those are defined inthe commands.cfg and only the values are given (separated by ! ) in the service.cfg.