Can you do fnd_request.submit_request from SQL Plus/Toad in Oracle?

You will need to initialize the global variables first using

fnd_global.apps_initialize(user_id => :user_id,
resp_id => :resp_id,
resp_appl_id => :resp_appl_id,
security_id => :security_id,
server_id => :server_id);

By doing the above, your global variables upon which Concurrent Managers depend upon will be populated. This will be equivalent to logging into Oracle Apps and submitting the concurrent request from a responsibility.