Generally speaking, if you have a library of SAS Autocall macro programs (let's say you had some macro programs for daily versus weekly processing...then you might have a SAS program with code like this:
%if (condition for daily processing) %then %do;
%else %if (condition for weekly processing) %then %do;
The macro program does not define the %DAILY or the %WEEKLY macro programs, it just calls them from the autocall macro location on your BI server.
Or, if you have the job scheduler set up and implemented in your configuration, there are ways to submit multiple jobs and define job dependencies.
Again, the best resource for your questions is the Platform Administration or Job Scheduler documentation and/or the Data Integration Studio class or the Data Integration Fast Track class or consulting Tech Support.
In the current release there is limited support for nesting jobs. By using Loop and Loop end transformations you can conditionally call/loop one other DI Studio job. I believe there will some more functionality in this area with 9.2 version.
But you can whatever you like by using the Cynthia mention, but then It won't be a DI Studio process.
But they can still put the code block with the macro call in the flow. And/or they can put it in a SP and turn the SP into a DI studio job. But generally when it comes down to questions like this, I always have to go back to the beginning and ask -- what is the situation that leads needing a job within a job? Examine those conditions and requirements and see whether there is another approach that would work equally well.