Escape Velocity is not OS X native. Escape Velocity requires a Macintosh running OS 7, 8 or 9. At the present time, we have no plans to port Escape Velocity to OS X.
Escape Velocity and its sequel, EV:Override, have been released as plug-ins for EV Nova. EV Nova, available at http://www.ambrosiasw.com/games/evn/ has been ported to Windows and is also OS X native.
So if you are a registered owner of EV Nova, you can use EV Nova to play any and all of the Escape Velocity games on PC or on OS X.