A lot of the unique features that Metal Gear Solid 5: The Phantom Pain was originally going to have never quite made it into the final release. This includes the ability to interact with the other characters on Mother Base- a feature that was sadly gutted, but the vestiges of which still remain in the game’s code.
However, Metal Gear fans are a determined bunch, and they’ve managed to track down some of these characters- one of these is Ocelot, who can apparently be spotted at times on Mother Base while leaving on the chopper for a mission. It’s extremely hard to ever see him, especially since Ocelot only infrequently appears in an inaccessible spot as a small dot. A determined player, however, managed to get video footage of Ocelot on the Mother Base as Big Boss was leaving for a new mission. You can check it out for yourself below.
Source: Reddit.