In the U.S., the "airside" part of the terminal with arriving and departing domestic passengers freely intermingle under the therory that everyone has gone through security and have been 'sterile" since doing so.
For international flights, arriving passengers are segregated from everyone else until they have cleared Immigration. These passengers must claim their luggage and clear Customs even if they are transiting to another U.S. destination. At the exit to Customs they recheck their bags and exit into the "landside" or non-sterile part of the terminal.
At that point they must go back through security to enter the arrival and departure gate area to connect to their flight.
As for wheelchair passengers, I do not know of any U.S. airport where there are not lifts or other accomodations for wheelchairs on the route leading to Immigration. The Americans with Disabilities Act has made this mandatory in public and almost all business establisments in the U.S. for a number of years.