There is no on-campus housing for admitted students over the summer, that's correct. The MIT Admissions website says this about overnight visits:
Overnights in March and April are only for students who have been admitted. We encourage all admitted students to visit during our annual Campus Preview Weekend in the spring. Overnight visits are not available from May through September. |
If you know or can get in touch with someone who's a current student staying on campus over the summer, you can probably arrange informally to stay with them, but there is no official place for you to stay while you're visiting over the summer, except in a hotel.