There are no places on campus to rent or borrow a wheelchair. You will have to rent one from a medical supply store in Colorado Springs.
Yes, you can drive up near the chapel and let him out. However, Acceptance will take place on the parade field which is not at all by the chapel. However, there is a parking lot by the parade field. However, access to it is restricted as most parents have to park by the field house and walk up to the parade field which is a pretty good uphill trek. Maybe the lot by the parade field is reserved for handicap access. You would need to find out. I am sure they would let you drive up there, unload the wheelchair, and go park the care down by the field house if required.
Also, I can't remember if shuttle buses were running for Acceptance Day. I know they are for Parent's Weekend and then the shuttles can be caught right by the field house and ridden to different destinations on campus.