No, you have to recompress it in FCP, so it's not native. I don't recommend editing that way, as there's high rendering times and too much M2V video seems to crash the program anyway. Converting it to PhotoJPEG (in MPEG Streamclip) lets you edit more easily (though you pay for it in hard drive space - I had a tough decision between crashing or having less material to edit with when doing my 10 Doctors project).

I don't know of a way to edit M2V natively on Mac. MPEG Streamclip is very useful for cutting the part of a clip you want out, though ... the accuracy being within 15 frames as is the M2V standard. I often "edit" my M2Vs together in DVD Studio Pro - how I did Empire and Jedi classic.