Can I use the MAX32621 EV Kit to evaluate a MAX32620?

Yes, the MAX32621 EV Kit (MAX32621-EVKIT#) contains a socket.  The MAX32621 which ships with the EV Kit can be removed.  This allows multiple devices to be programmed/evaluated, including the MAX32620.  The EV Kit only comes with one MAX32621, so additional samples must be procured separately.