I think it is a good idea to have a separate job for your Robot Tests. You might want to launch your test even if there is no new build or deploy of your SUT (e.g. because you added a test).
So, if your Software under test is already deployed and up and running when your Robot Jenkins job starts, you still have to do a "source code management" step to download the source of your test on your slave in the workspace of your job. And then in the build section you will have a shell step that actually launch the Robot Tests.
If you get an error like
$ pybot mytest.txt
[ ERROR ] Parsing 'mytest.txt' failed: Data source does not exist.
Then it means your Robot tests were not downloaded on your slave in your workspace.