The Martian Manhunter Showcase (volume one) is supposed to contain his earliest stories from Detective Comics (issues #225 - 304, from 1955 to 1962). So, yes, he appears in both his human disguise and his usual green self.


There's an amusing overview of the period by Alan Kistler here:
www.monitorduty.com/mdarchives/2005/10/alan_kistlers_p_1.shtml

I'm looking forward to picking this one up this week.