Do unit arrays leak?

If i have filled an array with, say, 40 units, do the handles leak if i don't loop through the array, setting them to null?

It is the same as not nulling 40 separate unit variables, so yes, it would cause some memory leaks.

However, if you replace the array with new units, the old values will not "leak". They will be garbage collected normally by the engine. Leak is more for data that is lost and can never be recovered, vs data that is still accessible but hasn't been cleared yet.