My grade for course X has not yet been released, but I need to know whether I passed course X in order to enroll in course Y. Can I still enroll in course Y?

In general, the answer is yes. 

Minimum number of completed units

Some courses require to have previously completed a minimum number of units. In terms of determining whether you have met the prerequisite for this course, you can include in your counting of completed units the courses for which you have not yet received a grade.

Example: MMS 197 requires you to have finished a minimum of 72 academic units.

If you have successfully received a passing grade for 22 courses in the past, and you took 2 courses for which you haven't received a grade yet, can you enroll in MMS 197? 

The answer is yes, because even though you only have 22x3 = 66 completed units (which is fewer than the minimum required), you also have 2x3 = 6 pending units. Since 66 + 6 = 72, you can still enroll MMS 197.

However, if you receive failing grades in those two courses with missing grades before the enrollment period is finished, do not register for MMS 197; if you have already enrolled in MMS 197, you are requested to please apply for a Change of Matriculation. 

Completion of one course as a prerequisite for another

If course X is a prerequisite for course Y and your grade for course X has not been released by the enrollment period, you can still enroll in course Y. See the following example.

Example: MMS 141 requires you to have passed MMS 140. You previously took MMS 140 but have not yet been given a grade. The enrollment period has started and MMS 141 is being offered. You can still enroll in MMS 141.

However, if you receive a failing MMS 140 grade before the enrollment period is finished, do not register for MMS 141; if you have already enrolled in MMS 141 and you receive a failing grade, you are requested to please apply for a Change of Matriculation.