Yes and no. I think mzscheme's GC can handle it without explicitly calling free at the right time, but you have to register a "finalizer" function to do so. That function will be called when the GC collects the object.
It does not know the size of malloced objects however, so be careful (no pb there, but if you allocate something very big, mzscheme will only see a new reference and will not necessarily call GC when you will actually lack memory).
