@OhPearl I found the page you need to study about cross registration for MIT students at MassArt.
You cannot use any MassArt classes as your 8 required Humanities subjects to get an MIT degree. The courses you take at MassArt will be graded P/F. You can use Wellesley classes and I think Harvard classes for those 8 required humanities , HASS classes. You can cross register at Mass Art, though as long as you are a full time undergrad at MIT and earn elective credits, but I wonder how many you will realistically be able to take if you want to finish a degree at MIT in four years?
http://act.mit.edu/academic-program/cross-registration/for-mit-students/