Masks don't morph any pixels contained inside them, they really only change their shape. That doesn't mean that masks cannot be used as auxiliary shapes for actual morphing, but it will require effects like Reshape or commercial plug-ins like RE:Flex. Still, from your description it doesn't sound like it would be necessary. One would probably simply animate masks or shape layers for such geometric stuff, but it depends on the specifics. In any case, the more time you spend fancying this up in AI, the more time you waste in AE and the more complicated it becomes to do anything with it. Beyond prepping the shapes and using copy&paste to get them over to AE I wouldn#t use AI much. If it realyl is that simple, everything can be done just as well in AE.