There are several ways you can get both STDERR and STDOUT from a sub-process. perlipc covers some of them. There are also various process management modules available from CPAN that you might consider.

You can use kill to check whether a process is running or not, but you would need the process ID for that - you could add it to the output of dashboard.pl.

You may be able to use waitpid to wait for all processes in the process group to finish, if your system supports this.