I'm trying Nemo 1.1.2, under Mate and I think I will switch to that.
I don't know how to change the default file manager though - the one that is opened by folder launchers on a Mate panel. I have been using Nautilus 3.4, which registered itself as the default file manager when I installed Cinnamon on the side.
I know how to change the file manager that draws the desktop icons, it's a separate setting and is in dconf-editor. Or was it gconf-editor. I can't find the setting anymore actually.
I think Nemo can well become Mate's default file manager, as it's not stagnating and looks good (even Nautilus looks good but Nemo has a much better toolbar). Unless you consider there are too many dependencies.
I'd use Caja, but the gtk3 remakes look much better to me and with Nemo there's no compromise