Both ways are possible. In Captivate 6 it is easier to have a pretest and a 'real' assessment at the end, but you are not talking about that last one?
Also: some functionality could be taken over by the LMS, depending on its possibilities. Just an example (I'm teacher in a college): I can offer an assessment (pretest), and if the student fails, will show the training modules using the LMS, whereas for success this shouldn't be necessary. The same assessment used as pretest can also be re-used as final test.
I concur with Lieve. A Captivate SCORM module cannot MAKE itself mandatory to force the user to take it. That's something that has to be controlled by the course delivery system.
Think of the course as being vegetables and your mother as being the LMS. Whether or not you had to eat your vegies was not decided by the pumpkin.
If the pretest is a separate module to the main content and assessment, then whether this gets disabled or not is also going to be something decided by the LMS. However, if you are using the new Pretest functionality offered in Cp6 and everything is inside the same project file, then you would be able to control whether or not the user was able to redo the pretest from within the course module itself. But this assumes that whatever the condition is that determines the availability of the pretest is something that is also found within the module.